Vulnerability · Published May 27, 2026 · Assigned by EEF
CVE-2026-42791OCSP responder certificate validity period not checked in public_key
Medium 6.3
In plain English
A medium-severity improper certificate validation in OTP from Erlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | erlang | 1:27.3.4.1+dfsg-1+deb13u3 | DEBIAN-CVE-2026-42791 |
| Debian:14 | erlang | 1:27.3.4.12+dfsg-1 | DEBIAN-CVE-2026-42791 |
| Ubuntu:22.04:LTS | erlang | 1:24.2.1+dfsg-1ubuntu0.8 | USN-8901-1 |
| Ubuntu:24.04:LTS | erlang | 1:25.3.2.8+dfsg-1ubuntu4.8 | USN-8901-1 |
| Ubuntu:25.10 | erlang | no fix listed | UBUNTU-CVE-2026-42791 |
| Ubuntu:26.04:LTS | erlang | 1:27.3.4.6+dfsg-1ubuntu0.2 | USN-8901-1 |
| Ubuntu:26.04:LTS | erlang | 1:27.3.4.6+dfsg-1ubuntu0.2 | UBUNTU-CVE-2026-42791 |
Affected products (as reported)
Weakness: CWE-295, CWE-672 · Vector: 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
References
- https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fff vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-42791.html related
- https://osv.dev/vulnerability/EEF-CVE-2026-42791 related
- https://www.erlang.org/doc/system/versions.html#order-of-versions x_version-scheme
- https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b patch
- https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76 patch