CVE-2026-42791

Name	CVE-2026-42791
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 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.16 before 1.17.1.3, 1.20.3.1, and 1.21.1.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
erlang (PTS)	bullseye	1:23.2.6+dfsg-1+deb11u1	fixed
	bullseye (security)	1:23.2.6+dfsg-1+deb11u4	fixed
	bookworm	1:25.2.3+dfsg-1+deb12u4	fixed
	bookworm (security)	1:25.2.3+dfsg-1+deb12u1	fixed
	trixie	1:27.3.4.1+dfsg-1+deb13u2	vulnerable
	forky	1:27.3.4.11+dfsg-7	vulnerable
	sid	1:27.3.4.12+dfsg-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version
erlang	source	bullseye	(not affected)
erlang	source	bookworm	(not affected)
erlang	source	(unstable)	1:27.3.4.12+dfsg-1

Notes

[bookworm] - erlang <not-affected> (Vulnerable code not present)
[bullseye] - erlang <not-affected> (Vulnerable code not present)
https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fff
https://cna.erlef.org/cves/CVE-2026-42791.html
https://osv.dev/vulnerability/EEF-CVE-2026-42791
https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b (OTP-27.3.4.12)
https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76 (OTP-29.0.1, OTP-28.5.0.1)