CVE-2026-42789
MediumCVSS 4.8Exploitation Probability (EPSS)
Low risk32th percentile - higher than 32% of all known CVEs
Summary
A vulnerability in the public_key module (pubkey_cert) of Erlang OTP involves improper following of a certificate's chain of trust. A certificate with basicConstraints cA:false and no keyUsage extension can be accepted as an intermediate issuer in a chain, enabling certificate chain forgery. This affects OTP from 17.0 before 27.3.4.19, 28.5.0.8, and 29.1.2.
Risk Assessment
Any party holding an end-entity certificate with cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can sign forged certificates for arbitrary identities. This affects all TLS and mTLS endpoints built on the OTP ssl application, including server identity verification on the client side and client certificate verification on mTLS servers.
Recommendation
Update Erlang OTP to version 27.3.4.19, 28.5.0.8, or 29.1.2 (public_key to 1.17.1.7, 1.20.3.6, or 1.21.8 respectively). Until patched, consider restricting trust for certificates lacking the keyUsage extension and monitor TLS/mTLS traffic for unusual certificate chains.
Other vulnerabilities in Erlang OTP public_key
See all- CVE-2026-59251High
A resource allocation vulnerability in Erlang/OTP's public_key certificate path validation allows a remote unauthenticated attacker to cause denial of service by sending a crafted X.509 certificate chain during TLS handshake. The certificate policy tree grows without bounds, exhausting BEAM schedulers and node memory, crashing the entire VM. This affects all TLS connections that validate peer certificates by default.
- CVE-2026-42790High
A vulnerability in the Erlang OTP public_key library allows bypassing DNS nameConstraints via subject CommonName fallback in TLS hostname verification. Two flaws enable a subordinate CA with restricted DNS nameConstraints to issue a leaf certificate accepted for an out-of-scope hostname.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS