UBUNTU-CVE-2026-42791 (CVE-2026-42791)

Vulnerability from osv_ubuntu – Published: 2026-05-27 14:16 – Updated: 2026-10-08 16:57 – Source website
VLAI
Details

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.

Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
N/A (UNKNOWN)
medium
References
To clipboard 

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  ],
  "aliases": [],
  "details": "Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case \u2014 server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP\u00a029.0.1, OTP\u00a028.5.0.1 and OTP\u00a027.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.",
  "id": "UBUNTU-CVE-2026-42791",
  "modified": "2026-10-08T16:57:23Z",
  "published": "2026-05-27T14:16:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-42791"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-42791"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fff"
    },
    {
      "type": "REPORT",
      "url": "https://cna.erlef.org/cves/CVE-2026-42791.html"
    },
    {
      "type": "REPORT",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-42791"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76"
    },
    {
      "type": "REPORT",
      "url": "https://www.erlang.org/doc/system/versions.html#order-of-versions"
    },
    {
      "type": "ADVISORY",
      "url": "https://ubuntu.com/security/notices/USN-8901-1"
    }
  ],
  "related": [
    "USN-8901-1"
  ],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    },
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-42791"
  ]
}



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