{"id":"UBUNTU-CVE-2026-42791","details":"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.","modified":"2026-10-08T19:46:17.474810174Z","published":"2026-05-27T14:16:00Z","related":["USN-8901-1"],"upstream":["CVE-2026-42791"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-42791"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-42791"},{"type":"REPORT","url":"https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fff"},{"type":"REPORT","url":"https://cna.erlef.org/cves/CVE-2026-42791.html"},{"type":"REPORT","url":"https://osv.dev/vulnerability/EEF-CVE-2026-42791"},{"type":"REPORT","url":"https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b"},{"type":"REPORT","url":"https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76"},{"type":"REPORT","url":"https://github.com/erlang/otp/commit/7995f1fdaee3da569bb810358ce0f546471d169b"},{"type":"REPORT","url":"https://github.com/erlang/otp/commit/b3870e02405c709a872b01ba6086065620cdfe76"},{"type":"REPORT","url":"https://www.erlang.org/doc/system/versions.html#order-of-versions"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-8901-1"}],"affected":[{"package":{"name":"erlang","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/erlang?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1:27.3+dfsg-1ubuntu1","1:27.3+dfsg-1ubuntu1.1","1:27.3.4.1+dfsg-1","1:27.3.4.1+dfsg-1build1","1:27.3.4.1+dfsg-1ubuntu0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"erlang","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-asn1","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-base","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-common-test"},{"binary_name":"erlang-crypto","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-debugger"},{"binary_name":"erlang-dialyzer","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-diameter","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-edoc","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-eldap","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-et","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-eunit","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-examples"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-ftp"},{"binary_name":"erlang-inets","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-jinterface","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-megaco","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-mnesia","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-mode","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-nox"},{"binary_name":"erlang-observer","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-odbc","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-os-mon","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-parsetools","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-public-key","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-reltool","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-runtime-tools"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-snmp"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-src"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-ssh"},{"binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1","binary_name":"erlang-ssl"},{"binary_name":"erlang-syntax-tools","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-tftp","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-tools","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-wx","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-x11","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"},{"binary_name":"erlang-xmerl","binary_version":"1:27.3.4.1+dfsg-1ubuntu0.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-42791.json"}},{"package":{"name":"erlang","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/erlang?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:27.3.4.6+dfsg-1ubuntu0.2"}]}],"versions":["1:27.3.4.1+dfsg-1build1","1:27.3.4.3+dfsg-1","1:27.3.4.4+dfsg-1","1:27.3.4.6+dfsg-1","1:27.3.4.6+dfsg-1ubuntu0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"erlang","binary_version":"1:27.3.4.6+dfsg-1ubuntu0.2"},{"binary_name":"erlang-asn1","binary_version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