CWE-757
AllowedSelection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
Abstraction: Base · Status: Incomplete
A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.
52 vulnerabilities reference this CWE, most recent first.
GHSA-VQ75-425F-VQ6R
Vulnerability from github – Published: 2022-05-24 17:28 – Updated: 2025-06-05 00:31Philips Clinical Collaboration Platform, Versions 12.2.1 and prior. The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an attacker to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
{
"affected": [],
"aliases": [
"CVE-2020-16200"
],
"database_specific": {
"cwe_ids": [
"CWE-757"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2020-09-18T18:15:00Z",
"severity": "MODERATE"
},
"details": "Philips Clinical Collaboration Platform, Versions 12.2.1 and prior. The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an attacker to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.",
"id": "GHSA-vq75-425f-vq6r",
"modified": "2025-06-05T00:31:18Z",
"published": "2022-05-24T17:28:58Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2020-16200"
},
{
"type": "WEB",
"url": "https://us-cert.cisa.gov/ics/advisories/icsma-20-261-01"
},
{
"type": "WEB",
"url": "https://www.philips.com/a-w/security/security-advisories/product-security-2020.html#2020_archive"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-WJ64-GH9J-XM82
Vulnerability from github – Published: 2026-03-13 21:31 – Updated: 2026-03-17 18:30Issue summary: An OpenSSL TLS 1.3 server may fail to negotiate the expected preferred key exchange group when its key exchange group configuration includes the default by using the 'DEFAULT' keyword.
Impact summary: A less preferred key exchange may be used even when a more preferred group is supported by both client and server, if the group was not included among the client's initial predicated keyshares. This will sometimes be the case with the new hybrid post-quantum groups, if the client chooses to defer their use until specifically requested by the server.
If an OpenSSL TLS 1.3 server's configuration uses the 'DEFAULT' keyword to interpolate the built-in default group list into its own configuration, perhaps adding or removing specific elements, then an implementation defect causes the 'DEFAULT' list to lose its 'tuple' structure, and all server-supported groups were treated as a single sufficiently secure 'tuple', with the server not sending a Hello Retry Request (HRR) even when a group in a more preferred tuple was mutually supported.
As a result, the client and server might fail to negotiate a mutually supported post-quantum key agreement group, such as 'X25519MLKEM768', if the client's configuration results in only 'classical' groups (such as 'X25519' being the only ones in the client's initial keyshare prediction).
OpenSSL 3.5 and later support a new syntax for selecting the most preferred TLS 1.3 key agreement group on TLS servers. The old syntax had a single 'flat' list of groups, and treated all the supported groups as sufficiently secure. If any of the keyshares predicted by the client were supported by the server the most preferred among these was selected, even if other groups supported by the client, but not included in the list of predicted keyshares would have been more preferred, if included.
The new syntax partitions the groups into distinct 'tuples' of roughly equivalent security. Within each tuple the most preferred group included among the client's predicted keyshares is chosen, but if the client supports a group from a more preferred tuple, but did not predict any corresponding keyshares, the server will ask the client to retry the ClientHello (by issuing a Hello Retry Request or HRR) with the most preferred mutually supported group.
The above works as expected when the server's configuration uses the built-in default group list, or explicitly defines its own list by directly defining the various desired groups and group 'tuples'.
No OpenSSL FIPS modules are affected by this issue, the code in question lies outside the FIPS boundary.
OpenSSL 3.6 and 3.5 are vulnerable to this issue.
OpenSSL 3.6 users should upgrade to OpenSSL 3.6.2 once it is released. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.6 once it is released.
OpenSSL 3.4, 3.3, 3.0, 1.0.2 and 1.1.1 are not affected by this issue.
{
"affected": [],
"aliases": [
"CVE-2026-2673"
],
"database_specific": {
"cwe_ids": [
"CWE-757"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-03-13T19:54:34Z",
"severity": "HIGH"
},
"details": "Issue summary: An OpenSSL TLS 1.3 server may fail to negotiate the expected\npreferred key exchange group when its key exchange group configuration includes\nthe default by using the \u0027DEFAULT\u0027 keyword.\n\nImpact summary: A less preferred key exchange may be used even when a more\npreferred group is supported by both client and server, if the group\nwas not included among the client\u0027s initial predicated keyshares.\nThis will sometimes be the case with the new hybrid post-quantum groups,\nif the client chooses to defer their use until specifically requested by\nthe server.\n\nIf an OpenSSL TLS 1.3 server\u0027s configuration uses the \u0027DEFAULT\u0027 keyword to\ninterpolate the built-in default group list into its own configuration, perhaps\nadding or removing specific elements, then an implementation defect causes the\n\u0027DEFAULT\u0027 list to lose its \u0027tuple\u0027 structure, and all server-supported groups\nwere treated as a single sufficiently secure \u0027tuple\u0027, with the server not\nsending a Hello Retry Request (HRR) even when a group in a more preferred tuple\nwas mutually supported.\n\nAs a result, the client and server might fail to negotiate a mutually supported\npost-quantum key agreement group, such as \u0027X25519MLKEM768\u0027, if the client\u0027s\nconfiguration results in only \u0027classical\u0027 groups (such as \u0027X25519\u0027 being the\nonly ones in the client\u0027s initial keyshare prediction).\n\nOpenSSL 3.5 and later support a new syntax for selecting the most preferred TLS\n1.3 key agreement group on TLS servers. The old syntax had a single \u0027flat\u0027\nlist of groups, and treated all the supported groups as sufficiently secure.\nIf any of the keyshares predicted by the client were supported by the server\nthe most preferred among these was selected, even if other groups supported by\nthe client, but not included in the list of predicted keyshares would have been\nmore preferred, if included.\n\nThe new syntax partitions the groups into distinct \u0027tuples\u0027 of roughly\nequivalent security. Within each tuple the most preferred group included among\nthe client\u0027s predicted keyshares is chosen, but if the client supports a group\nfrom a more preferred tuple, but did not predict any corresponding keyshares,\nthe server will ask the client to retry the ClientHello (by issuing a Hello\nRetry Request or HRR) with the most preferred mutually supported group.\n\nThe above works as expected when the server\u0027s configuration uses the built-in\ndefault group list, or explicitly defines its own list by directly defining the\nvarious desired groups and group \u0027tuples\u0027.\n\nNo OpenSSL FIPS modules are affected by this issue, the code in question lies\noutside the FIPS boundary.\n\nOpenSSL 3.6 and 3.5 are vulnerable to this issue.\n\nOpenSSL 3.6 users should upgrade to OpenSSL 3.6.2 once it is released.\nOpenSSL 3.5 users should upgrade to OpenSSL 3.5.6 once it is released.\n\nOpenSSL 3.4, 3.3, 3.0, 1.0.2 and 1.1.1 are not affected by this issue.",
"id": "GHSA-wj64-gh9j-xm82",
"modified": "2026-03-17T18:30:32Z",
"published": "2026-03-13T21:31:46Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-2673"
},
{
"type": "WEB",
"url": "https://github.com/openssl/openssl/commit/2157c9d81f7b0bd7dfa25b960e928ec28e8dd63f"
},
{
"type": "WEB",
"url": "https://github.com/openssl/openssl/commit/85977e013f32ceb96aa034c0e741adddc1a05e34"
},
{
"type": "WEB",
"url": "https://openssl-library.org/news/secadv/20260313.txt"
},
{
"type": "WEB",
"url": "http://www.openwall.com/lists/oss-security/2026/03/13/3"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
]
}
No mitigation information available for this CWE.
CAPEC-220: Client-Server Protocol Manipulation
An adversary takes advantage of weaknesses in the protocol by which a client and server are communicating to perform unexpected actions. Communication protocols are necessary to transfer messages between client and server applications. Moreover, different protocols may be used for different types of interactions.
CAPEC-606: Weakening of Cellular Encryption
An attacker, with control of a Cellular Rogue Base Station or through cooperation with a Malicious Mobile Network Operator can force the mobile device (e.g., the retransmission device) to use no encryption (A5/0 mode) or to use easily breakable encryption (A5/1 or A5/2 mode).
CAPEC-620: Drop Encryption Level
An attacker forces the encryption level to be lowered, thus enabling a successful attack against the encrypted data.