Description (CNA)
Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery. In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement. Any party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can use that certificate's private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers. This issue affects OTP from OTP 17.0 before OTP 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to public_key from 0.22 before 1.17.1.7, 1.20.3.6, and 1.21.8. Whether OTP before OTP 17.0, corresponding to public_key before 0.22, is affected is unknown.
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| Erlang / OTP | affected 17.0 before * |
| Erlang / OTP | affected 0.22 before * |
| Erlang / OTP | affected 84adefa331c4159d432d22840663c38f155cd4c1 before *; unaffected 0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8 before *; unaffected 75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333 before *; unaffected 82af606b5437c4de1276dbcc8855a47e88231226 before * |
CWE
CWE-295, CWE-296
References
- https://github.com/erlang/otp/security/advisories/GHSA-c99q-jmpx-v8qq
- https://cna.erlef.org/cves/CVE-2026-42789.html
- https://osv.dev/vulnerability/EEF-CVE-2026-42789
- https://www.erlang.org/doc/system/versions.html#order-of-versions
- https://github.com/erlang/otp/commit/0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8
- https://github.com/erlang/otp/commit/75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333
- https://github.com/erlang/otp/commit/82af606b5437c4de1276dbcc8855a47e88231226
ADP enrichment
No English description supplied.
No references supplied.
A flaw was found in Erlang OTP's public_key module. This vulnerability (CWE-295), related to improper certificate validation, allows a non-Certificate Authority (CA) certificate to be accepted as an intermediate issuer. A remote attacker, holding an end-entity certificate issued by a trusted CA, can exploit this by forging leaf certificates for arbitrary identities. This can lead to compromised server identity verification on the client side and client certificate verification on mutual Transport Layer Security (mTLS) servers, undermining the trust in certificate-based authentication.