Erlang OTP pubkey_ocsp.erl certificate validation

Summaryinfo

A vulnerability labeled as problematic has been found in Erlang OTP. Affected is an unknown function in the library lib/public_key/src/pubkey_ocsp.erl. Executing a manipulation can lead to certificate validation. This vulnerability is handled as CVE-2026-42791. The attack can be executed remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in Erlang OTP (the affected version unknown) and classified as problematic. This vulnerability affects an unknown part in the library lib/public_key/src/pubkey_ocsp.erl. The manipulation with an unknown input leads to a certificate validation vulnerability. The CWE definition for the vulnerability is CWE-295. The product does not validate, or incorrectly validates, a certificate. As an impact it is known to affect integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-42791 since 04/29/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1587.003.

Upgrading eliminates this vulnerability. Applying the patch 7995f1fdaee3da569bb810358ce0f546471d169b is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• Erlang

Name

• OTP

License

• open-source

Website

• Product: https://github.com/erlang/otp/

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