Erlang security advisory (AV26-948)

A remote unauthenticated denial of service vulnerability exists in the Erlang/OTP asn1 OBJECT IDENTIFIER decoder. It causes quadratic computational work during TLS handshake when a crafted OID is sent, potentially crashing services. This flaw affects OTP and asn1 versions prior to specific fixes, and can be triggered during certificate parsing. Attackers can exploit this to crash services without authentication, impacting TLS clients and mutual-TLS servers. Current exploitation status is unknown as no public PoC is known.

Do: Upgrade to OTP 27.3.4.18, 28.5.0.7, and 29.1.1 to mitigate the vulnerability. Implement strict TLS certificate validation and disable TLS handshake parsing in vulnerable components. Monitor OTP versions for known vulnerabilities.

CVE-2026-89422 exposes Erlang/OTP ssl with a Key Exchange without Entity Authentication flaw. A TLS 1.3 client connection can be impersonated by answering a pre_shared_key extension the server never offered, causing the handshake to complete without validating the server certificate. This bypasses certificate validation, hostname verification, partial chain checking, CRL checking, and OCSP stapling, allowing an attacker to establish a valid-looking connection against a certificate-less, key-less peer. The vulnerability affects all default client configurations and is not restricted to TLS 1.2 clients. No public exploit is known, and the issue is reported as critical with no confirmed exploitation.

Do: Upgrade all affected Erlang/OTP ssl versions to the latest fixed release; disable TLS 1.3 with PSK extensions or restrict clients to TLS 1.2; verify certificate and hostname validation; monitor for resumption-based impersonation and certificate validation bypass.