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PYSEC-2019-136
Vulnerability from pysec - Published: 2019-12-20 23:15 - Updated: 2020-02-25 17:15
VLAI
Details
Waitress through version 1.3.1 implemented a "MAY" part of the RFC7230 which states: "Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR." Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. This issue is fixed in Waitress 1.4.0.
Impacted products
| Name | purl | waitress | pkg:pypi/waitress |
|---|
Aliases
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "waitress",
"purl": "pkg:pypi/waitress"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
}
],
"repo": "https://github.com/Pylons/waitress",
"type": "GIT"
},
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.4.0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"0.1",
"0.2",
"0.3",
"0.4",
"0.5",
"0.6",
"0.6.1",
"0.7",
"0.8",
"0.8.1",
"0.8.2",
"0.8.3",
"0.8.4",
"0.8.5",
"0.8.6",
"0.8.7",
"0.8.8",
"0.8.9",
"0.8.10",
"0.8.11b0",
"0.9.0b0",
"0.9.0b1",
"0.9.0",
"1.0a1",
"1.0a2",
"1.0.0",
"1.0.1",
"1.0.2",
"1.1.0",
"1.2.0b1",
"1.2.0b2",
"1.2.0b3",
"1.2.0",
"1.2.1",
"1.3.0b0",
"1.3.0",
"1.3.1"
]
}
],
"aliases": [
"CVE-2019-16785",
"GHSA-pg36-wpm5-g57p"
],
"details": "Waitress through version 1.3.1 implemented a \"MAY\" part of the RFC7230 which states: \"Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR.\" Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. This issue is fixed in Waitress 1.4.0.",
"id": "PYSEC-2019-136",
"modified": "2020-02-25T17:15:00Z",
"published": "2019-12-20T23:15:00Z",
"references": [
{
"type": "ADVISORY",
"url": "https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p"
},
{
"type": "FIX",
"url": "https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
},
{
"type": "WEB",
"url": "https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7/"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5/"
},
{
"type": "ADVISORY",
"url": "https://access.redhat.com/errata/RHSA-2020:0720"
}
]
}
BREW-BACKGROUNDREMOVER-C… (GHSA-PG36-WPM5-G57P)
Vulnerability from osv_homebrew – Published: 2026-08-13 16:37 – Updated: 2026-09-09 23:43 – Source website
VLAI
Summary
HTTP Request Smuggling: LF vs CRLF handling in Waitress
Details
Impact
Waitress implemented a "MAY" part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:
Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.
Example:
Content-Length: 100[CRLF]
X-Header: x[LF]Content-Length: 0[CRLF]
Would get treated by Waitress as if it were:
Content-Length: 100
X-Header: x
Content-Length: 0
This could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.
Patches
This issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies.
Waitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.
The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.
Workarounds
Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)
Issues/more security issues:
- open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)
- email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)
Severity
References
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "waitress",
"resource_purl": "pkg:pypi/waitress@3.0.2",
"upstream_fixed_in": "1.4.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "backgroundremover",
"purl": "pkg:brew/backgroundremover"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.4.5"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/waitress@3.0.2",
"name": "waitress",
"resource": "waitress",
"strategy": "registry",
"subject_version": "3.0.2"
}
]
},
"details": "### Impact\n\nWaitress implemented a \u0026amp;quot;MAY\u0026amp;quot; part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:\n\n Although the line terminator for the start-line and header fields is\n the sequence CRLF, a recipient MAY recognize a single LF as a line\n terminator and ignore any preceding CR.\n\nUnfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.\n\nExample:\n\n```\nContent-Length: 100[CRLF]\nX-Header: x[LF]Content-Length: 0[CRLF]\n```\n\nWould get treated by Waitress as if it were:\n\n```\nContent-Length: 100\nX-Header: x\nContent-Length: 0\n```\n\nThis could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.\n\n\n### Patches\n\nThis issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies. \n\nWaitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.\n\nThe Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don\u0026amp;#39;t cause any changes in behavior.\n\n### Workarounds\n\nVarious reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn\u0026amp;#39;t use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)\n\n### Issues/more security issues:\n\n* open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)\n* email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)",
"id": "BREW-backgroundremover-CVE-2019-16785",
"modified": "2026-09-09T23:43:06Z",
"published": "2026-08-13T16:37:03Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-16785"
},
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2020:0720"
},
{
"type": "WEB",
"url": "https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"
},
{
"type": "PACKAGE",
"url": "https://github.com/Pylons/waitress"
},
{
"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2019-136.yaml"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5"
},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpuapr2022.html"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "HTTP Request Smuggling: LF vs CRLF handling in Waitress",
"upstream": [
"GHSA-pg36-wpm5-g57p",
"CVE-2019-16785",
"PYSEC-2019-136"
]
}
BREW-ICLOUDPD-CVE-2019-16785 (GHSA-PG36-WPM5-G57P)
Vulnerability from osv_homebrew – Published: 2026-08-13 16:59 – Updated: 2026-09-10 00:11 – Source website
VLAI
Summary
HTTP Request Smuggling: LF vs CRLF handling in Waitress
Details
Impact
Waitress implemented a "MAY" part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:
Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.
Example:
Content-Length: 100[CRLF]
X-Header: x[LF]Content-Length: 0[CRLF]
Would get treated by Waitress as if it were:
Content-Length: 100
X-Header: x
Content-Length: 0
This could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.
Patches
This issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies.
Waitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.
The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.
Workarounds
Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)
Issues/more security issues:
- open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)
- email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)
Severity
References
| URL | Type | ||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||||||||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "waitress",
"resource_purl": "pkg:pypi/waitress@3.0.2",
"upstream_fixed_in": "1.4.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "icloudpd",
"purl": "pkg:brew/icloudpd"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.32.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/waitress@3.0.2",
"name": "waitress",
"resource": "waitress",
"strategy": "registry",
"subject_version": "3.0.2"
}
]
},
"details": "### Impact\n\nWaitress implemented a \u0026amp;quot;MAY\u0026amp;quot; part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:\n\n Although the line terminator for the start-line and header fields is\n the sequence CRLF, a recipient MAY recognize a single LF as a line\n terminator and ignore any preceding CR.\n\nUnfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.\n\nExample:\n\n```\nContent-Length: 100[CRLF]\nX-Header: x[LF]Content-Length: 0[CRLF]\n```\n\nWould get treated by Waitress as if it were:\n\n```\nContent-Length: 100\nX-Header: x\nContent-Length: 0\n```\n\nThis could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.\n\n\n### Patches\n\nThis issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies. \n\nWaitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.\n\nThe Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don\u0026amp;#39;t cause any changes in behavior.\n\n### Workarounds\n\nVarious reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn\u0026amp;#39;t use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)\n\n### Issues/more security issues:\n\n* open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)\n* email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)",
"id": "BREW-icloudpd-CVE-2019-16785",
"modified": "2026-09-10T00:11:17Z",
"published": "2026-08-13T16:59:03Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-16785"
},
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2020:0720"
},
{
"type": "WEB",
"url": "https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"
},
{
"type": "PACKAGE",
"url": "https://github.com/Pylons/waitress"
},
{
"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2019-136.yaml"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5"
},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpuapr2022.html"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "HTTP Request Smuggling: LF vs CRLF handling in Waitress",
"upstream": [
"GHSA-pg36-wpm5-g57p",
"CVE-2019-16785",
"PYSEC-2019-136"
]
}
BREW-MKTXP-CVE-2019-16785 (GHSA-PG36-WPM5-G57P)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:14 – Updated: 2026-09-10 00:32 – Source website
VLAI
Summary
HTTP Request Smuggling: LF vs CRLF handling in Waitress
Details
Impact
Waitress implemented a "MAY" part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:
Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.
Example:
Content-Length: 100[CRLF]
X-Header: x[LF]Content-Length: 0[CRLF]
Would get treated by Waitress as if it were:
Content-Length: 100
X-Header: x
Content-Length: 0
This could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.
Patches
This issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies.
Waitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.
The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.
Workarounds
Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)
Issues/more security issues:
- open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)
- email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)
Severity
References
| URL | Type | ||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||||||||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "waitress",
"resource_purl": "pkg:pypi/waitress@3.0.2",
"upstream_fixed_in": "1.4.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "mktxp",
"purl": "pkg:brew/mktxp"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.2.19"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/waitress@3.0.2",
"name": "waitress",
"resource": "waitress",
"strategy": "registry",
"subject_version": "3.0.2"
}
]
},
"details": "### Impact\n\nWaitress implemented a \u0026amp;quot;MAY\u0026amp;quot; part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:\n\n Although the line terminator for the start-line and header fields is\n the sequence CRLF, a recipient MAY recognize a single LF as a line\n terminator and ignore any preceding CR.\n\nUnfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.\n\nExample:\n\n```\nContent-Length: 100[CRLF]\nX-Header: x[LF]Content-Length: 0[CRLF]\n```\n\nWould get treated by Waitress as if it were:\n\n```\nContent-Length: 100\nX-Header: x\nContent-Length: 0\n```\n\nThis could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.\n\n\n### Patches\n\nThis issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies. \n\nWaitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.\n\nThe Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don\u0026amp;#39;t cause any changes in behavior.\n\n### Workarounds\n\nVarious reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn\u0026amp;#39;t use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)\n\n### Issues/more security issues:\n\n* open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)\n* email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)",
"id": "BREW-mktxp-CVE-2019-16785",
"modified": "2026-09-10T00:32:14Z",
"published": "2026-08-13T17:14:17Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-16785"
},
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2020:0720"
},
{
"type": "WEB",
"url": "https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"
},
{
"type": "PACKAGE",
"url": "https://github.com/Pylons/waitress"
},
{
"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2019-136.yaml"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5"
},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpuapr2022.html"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N",
"type": "CVSS_V4"
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],
"summary": "HTTP Request Smuggling: LF vs CRLF handling in Waitress",
"upstream": [
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]
}
CVE-2019-16785 (GCVE-0-2019-16785)
Vulnerability from cvelistv5 – Published: 2019-12-20 23:00 – Updated: 2024-08-05 01:24
VLAI
EPSS
VEX
Title
HTTP Request Smuggling: LF vs CRLF handling in Waitress
Summary
Waitress through version 1.3.1 implemented a "MAY" part of the RFC7230 which states: "Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR." Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. This issue is fixed in Waitress 1.4.0.
Severity
7.1 (High)
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
Assigner
References
8 references
| URL | Tags |
|---|---|
| https://lists.fedoraproject.org/archives/list/pac… | vendor-advisoryx_refsource_FEDORA |
| https://lists.fedoraproject.org/archives/list/pac… | vendor-advisoryx_refsource_FEDORA |
| https://access.redhat.com/errata/RHSA-2020:0720 | vendor-advisoryx_refsource_REDHAT |
| https://www.oracle.com/security-alerts/cpuapr2022.html | x_refsource_MISC |
| https://docs.pylonsproject.org/projects/waitress/… | x_refsource_MISC |
| https://github.com/Pylons/waitress/security/advis… | x_refsource_CONFIRM |
| https://github.com/Pylons/waitress/commit/8eba394… | x_refsource_MISC |
| https://lists.debian.org/debian-lts-announce/2022… | mailing-listx_refsource_MLIST |
Impacted products
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GHSA-PG36-WPM5-G57P
Vulnerability from github – Published: 2019-12-20 23:03 – Updated: 2024-11-19 13:55
VLAI
Summary
HTTP Request Smuggling: LF vs CRLF handling in Waitress
Details
Impact
Waitress implemented a "MAY" part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:
Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.
Example:
Content-Length: 100[CRLF]
X-Header: x[LF]Content-Length: 0[CRLF]
Would get treated by Waitress as if it were:
Content-Length: 100
X-Header: x
Content-Length: 0
This could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.
Patches
This issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies.
Waitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.
The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.
Workarounds
Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)
Issues/more security issues:
- open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)
- email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)
Severity
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "waitress"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.4.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2019-16785"
],
"database_specific": {
"cwe_ids": [
"CWE-444"
],
"github_reviewed": true,
"github_reviewed_at": "2019-12-20T23:01:44Z",
"nvd_published_at": "2019-12-20T23:15:00Z",
"severity": "MODERATE"
},
"details": "### Impact\n\nWaitress implemented a \u0026amp;quot;MAY\u0026amp;quot; part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:\n\n Although the line terminator for the start-line and header fields is\n the sequence CRLF, a recipient MAY recognize a single LF as a line\n terminator and ignore any preceding CR.\n\nUnfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.\n\nExample:\n\n```\nContent-Length: 100[CRLF]\nX-Header: x[LF]Content-Length: 0[CRLF]\n```\n\nWould get treated by Waitress as if it were:\n\n```\nContent-Length: 100\nX-Header: x\nContent-Length: 0\n```\n\nThis could potentially get used by attackers to split the HTTP request and smuggle a second request in the body of the first.\n\n\n### Patches\n\nThis issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies. \n\nWaitress no longer implements the MAY part of the specification and instead requires that all lines are terminated correctly with CRLF. If any lines are found with a bare CR or LF a 400 Bad Request is sent back to the requesting entity.\n\nThe Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don\u0026amp;#39;t cause any changes in behavior.\n\n### Workarounds\n\nVarious reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn\u0026amp;#39;t use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method)\n\n### Issues/more security issues:\n\n* open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)\n* email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)",
"id": "GHSA-pg36-wpm5-g57p",
"modified": "2024-11-19T13:55:58Z",
"published": "2019-12-20T23:03:57Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-16785"
},
{
"type": "WEB",
"url": "https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2020:0720"
},
{
"type": "WEB",
"url": "https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"
},
{
"type": "PACKAGE",
"url": "https://github.com/Pylons/waitress"
},
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"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2019-136.yaml"
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"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"
},
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"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7"
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},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpuapr2022.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "HTTP Request Smuggling: LF vs CRLF handling in Waitress"
}
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Trend slope:
-
(linear fit over daily sighting counts)
Show additional events:
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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