Improper Certificate Validation vulnerability in Erlang OTP publickey (pubkeyocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid.
OCSP response verification in pubkeyocsp:verifyresponse/5 and pubkeyocsp:isauthorizedresponder/3 in lib/publickey/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 publickey:pkixocsp_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.
{
"cwe_ids": [
"CWE-295",
"CWE-672"
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42791.json",
"unresolved_ranges": [
{
"extracted_events": [
{
"introduced": "1.16"
},
{
"fixed": "*"
},
{
"introduced": "27.0"
},
{
"fixed": "*"
},
{
"introduced": "2b1a742c651b90f8a7a1fb2ddde73f29915ea376"
},
{
"fixed": "*"
}
],
"source": "AFFECTED_FIELD"
}
],
"cna_assigner": "EEF"
}{
"cpe": "cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*",
"extracted_events": [
{
"introduced": "27.0"
},
{
"fixed": "27.3.4.12"
},
{
"introduced": "28.0"
},
{
"fixed": "28.5.0.1"
},
{
"introduced": "29.0"
},
{
"fixed": "29.0.1"
}
],
"source": [
"CPE_RANGE",
"REFERENCES"
]
}