GHSA-9F9V-4H96-WH6M
Vulnerability from github – Published: 2026-09-13 06:33 – Updated: 2026-09-13 06:33An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5. Exploitation requires an HTTP/3 frontend: HAProxy must be built with QUIC support and configured with a QUIC bind listener, and the affected traffic must reach a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Under those conditions, when an HTTP/3 request carries no Content-Length header, the HTTP/3 multiplexer credits the length declared in a DATA frame header to the stream endpoint's known-input-payload estimate at the moment the frame header is decoded, before the payload has been received, and that declared length is emitted verbatim as the HTTP/1.1 chunk size. A remote unauthenticated client that declares more payload than it delivers and then ends the stream causes HAProxy to announce a chunk larger than the bytes it writes and to return the connection to the idle pool in a desynchronized state. The result is potential HTTP request smuggling on reused backend connections: an attacker can place a request past a frontend rule such as a path-based http-request deny, so that the smuggled request is never seen by HAProxy's HTTP analysis, and can cause concurrent clients' requests, including their request lines and Authorization headers, to be consumed as the attacker's request body and lost. Exploitation is not deterministic; it depends on a race with backend connection pooling, succeeding in a majority of but not all trials during testing, and can be retried freely. The mechanism was introduced in 3.3-dev10; releases 3.2.x and earlier are unaffected.
{
"affected": [],
"aliases": [
"CVE-2026-90678"
],
"database_specific": {
"cwe_ids": [
"CWE-130"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-13T04:17:25Z",
"severity": "HIGH"
},
"details": "An issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5. Exploitation requires an HTTP/3 frontend: HAProxy must be built with QUIC support and configured with a QUIC bind listener, and the affected traffic must reach a backend over HTTP/1.1 using chunked transfer coding on a reused connection. Under those conditions, when an HTTP/3 request carries no Content-Length header, the HTTP/3 multiplexer credits the length declared in a DATA frame header to the stream endpoint\u0027s known-input-payload estimate at the moment the frame header is decoded, before the payload has been received, and that declared length is emitted verbatim as the HTTP/1.1 chunk size. A remote unauthenticated client that declares more payload than it delivers and then ends the stream causes HAProxy to announce a chunk larger than the bytes it writes and to return the connection to the idle pool in a desynchronized state. The result is potential HTTP request smuggling on reused backend connections: an attacker can place a request past a frontend rule such as a path-based http-request deny, so that the smuggled request is never seen by HAProxy\u0027s HTTP analysis, and can cause concurrent clients\u0027 requests, including their request lines and Authorization headers, to be consumed as the attacker\u0027s request body and lost. Exploitation is not deterministic; it depends on a race with backend connection pooling, succeeding in a majority of but not all trials during testing, and can be retried freely. The mechanism was introduced in 3.3-dev10; releases 3.2.x and earlier are unaffected.",
"id": "GHSA-9f9v-4h96-wh6m",
"modified": "2026-09-13T06:33:11Z",
"published": "2026-09-13T06:33:11Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90678"
},
{
"type": "WEB",
"url": "https://github.com/haproxy/haproxy/commit/86a4ebc761a278838e8cb06f3a292282ba704c65"
},
{
"type": "WEB",
"url": "https://www.haproxy.org/download/3.5/src/CHANGELOG"
},
{
"type": "WEB",
"url": "http://git.haproxy.org/?p=haproxy.git;a=commit;h=86a4ebc761a278838e8cb06f3a292282ba704c65"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:L",
"type": "CVSS_V3"
}
]
}
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.
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.