CVE-2026-42791 OCSP responder certificate validity period not checked in public_key
Attackers can bypass TLS certificate revocation checks by forging OCSP responses with expired responder keys, allowing revoked certificates to be accepted as valid.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42791?
CVE-2026-42791 is a medium-severity vulnerability in Erlang OTP, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2026-42791?
It affects 1 product.
Products include Erlang Erlang\/Otp.
How do I fix CVE-2026-42791?
Upgrade to a fixed version.
Is CVE-2026-42791 being exploited?
There is no known exploitation of CVE-2026-42791 in the wild and no public exploit code.
Other vulnerabilities in Erlang OTP
- CVE-2022-37026 Auth bypass in n/a
- CVE-2016-10253 Memory corruption in n/a
- CVE-2026-55953 TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication
- CVE-2026-49759 Stack buffer overflow in SCTP error cause parsing in inet_drv allows remote VM crash
- CVE-2026-58227 TLS/DTLS denial of service via unbounded recursion on cross-signed peer certificate chain
Sources
Also known as DEBIAN-CVE-2026-42791, EEF-CVE-2026-42791, GHSA-cjxj-wj6x-3fff, UBUNTU-CVE-2026-42791.