CVE-2026-55953 Erlang CVE debrief

Who should care

Users of Erlang/OTP versions prior to OTP 29.0.4, OTP 28.5.0.4, and OTP 27.3.4.15 should be aware of this vulnerability and take steps to mitigate it, especially those with on-path attacker exposure. This includes operators, platform administrators, vulnerability management teams, and security teams who need to assess the impact on their systems and plan for remediation.

Technical summary

The Erlang/OTP ssl TLS 1.2 (and earlier) and DTLS client does not verify that the cipher suite selected by the server in ServerHello was among the suites offered by the client in ClientHello. An on-path attacker between the client and the intended server can respond with a ServerHello selecting an anonymous key exchange suite such as TLS_DH_anon_* or TLS_ECDH_anon_* that the client never offered. This allows the attacker to bypass the verify_peer and cacerts configuration, making the entire handshake process vulnerable to eavesdropping and modification. The TLS 1.3 client path performs this check (per RFC 8446), so it is not affected.

Defensive priority

High

Recommended defensive actions

• Update to OTP 29.0.4, OTP 28.5.0.4, or OTP 27.3.4.15
• Verify and restrict cipher suites offered to servers
• Implement additional authentication and authorization mechanisms
• Monitor for suspicious activity
• Consider using TLS 1.3
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-27T16:17:49.500Z and has not been modified since. The NVD entry is currently Received. This issue is critical because it allows an on-path attacker to bypass verify_peer and cacerts configuration, making the entire handshake process vulnerable to eavesdropping and modification. The Erlang/OTP ssl TLS 1.2 (and earlier) and DTLS client does not verify that the cipher suite selected by the server in ServerHello was among the suites offered by the client in ClientHello. Users should verify their deployments and apply patches or mitigations as necessary.

Official resources