CVE-2026-42789
MediumCVSS 4.8Exploitation Probability (EPSS)
Low risk26th percentile - higher than 26% of all known CVEs
Summary
A vulnerability in the Erlang OTP public_key library (pubkey_cert module) allows improper following of a certificate's chain of trust. A non-CA certificate with basicConstraints cA:false and no keyUsage extension is incorrectly accepted as an intermediate issuer, enabling certificate chain forgery. Affected OTP versions: 17.0 through 29.0.1, 28.5.0.1, 27.3.4.12, and 26.2.5.21.
Risk Assessment
An attacker holding an end-entity certificate with cA:false and no keyUsage, issued by a trusted CA, can sign forged leaf certificates for arbitrary identities. This can compromise TLS/mTLS authentication, allowing impersonation of servers or clients and potential man-in-the-middle attacks.
Recommendation
Immediately upgrade Erlang OTP to version 29.0.1, 28.5.0.1, 27.3.4.12, or 26.2.5.21 depending on your branch. For systems that cannot be updated, consider temporarily disabling certificate chain validation in public_key or implementing additional verification controls.
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 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 0.22 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.