Weakness Type (CWE)

CWE-295 — CWE-295 Improper Certificate Validation

CAPEC

CVSS 4.0 Score

6.3

MEDIUM

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

Vulnerability 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.

Affected

pkg:otp/public_key

Module Source File Routine
pubkey_ocsp src/pubkey_ocsp.erl pubkey_ocsp:verify_response/5
pubkey_ocsp:is_authorized_responder/3
Status Type Version Changes / Fixed in
affected otp ⓘ 1.16
  • unaffected at 1.17.1.3
  • unaffected at 1.20.3.1
  • unaffected at 1.21.1

pkg:github/erlang/otp

Module Source File Routine
pubkey_ocsp lib/public_key/src/pubkey_ocsp.erl pubkey_ocsp:verify_response/5
pubkey_ocsp:is_authorized_responder/3
Status Type Version Changes / Fixed in
affected otp ⓘ 27.0
affected git ⓘ 2b1a742c65

Configurations

For the ssl application, OCSP stapling must be enabled by setting the stapling option to staple in the TLS client options. OCSP stapling is not enabled by default.<p>Applications calling public_key:pkix_ocsp_validate/5 directly are unconditionally affected when that function is used.</p>

Workarounds

  • For TLS clients using the ssl application, disable OCSP stapling by setting {stapling, no_staple} in the client options, or switch to CRL-based revocation checking with {crl_check, true}.
  • For applications calling public_key:pkix_ocsp_validate/5 directly, validate the responder certificate's validity period in application code before calling the function.

References

Credits

  • Remediation developer: Jakub Witczak
  • Remediation reviewer: Ingela Anderton Andin

CVE record as JSON:  GET /cves/CVE-2026-42791.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-42791.json