VulnerabilityModified

CVE-2026-42791

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.

MEDIUM 6.3EPSS 0.32%

Does this matter?

Lower severity and a low EPSS score (0.32%). Track it; it rarely justifies an emergency change on its own.

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.

CVSS 4.0: 6.3 MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.32% probability · 24th percentile
CISA KEV: Not listed
Weakness: CWE-295, CWE-672
Affected: erlang/erlang\/otp
Source: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

References

https://cna.erlef.org/cves/CVE-2026-42791.htmlThird Party Advisory
https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169bPatch
https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76Patch
https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fffMitigation, Vendor Advisory
https://osv.dev/vulnerability/EEF-CVE-2026-42791Third Party Advisory
https://www.erlang.org/doc/system/versions.html#order-of-versionsProduct

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.