CVE-2026-42789

Zwakheid

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,

Getroffen producten

• erlang erlang\/otp

Bronnen

• https://cna.erlef.org/cves/CVE-2026-42789.html
• https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db
• https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd
• https://github.com/erlang/otp/security/advisories/GHSA-c99q-jmpx-v8qq
• https://osv.dev/vulnerability/EEF-CVE-2026-42789
• https://www.erlang.org/doc/system/versions.html#order-of-versions