Erlang/OTP versions 17.0 through 29.0.3 are vulnerable to TLS downgrade attacks that allow an attacker to intercept and modify encrypted traffic.

The client-side TLS handshake logic in Erlang/OTP fails to validate that the cipher suite chosen by the server was among those offered by the client. An on-path attacker can force the use of anonymous key exchange suites, bypassing certificate validation and allowing for the interception or modification of traffic.

This vulnerability undermines the fundamental security of encrypted communications. If exploited, an attacker can perform man-in-the-middle attacks, leading to the exposure of sensitive data, credentials, or session tokens. Given the critical nature of TLS in protecting communications, a CVSS score of 9.1 reflects the severe risk to data confidentiality and integrity.

Immediate Action: Update Erlang/OTP to the latest patched version as specified in the vendor security advisory.

Proactive Monitoring: Monitor network traffic for unusual TLS handshake patterns, specifically the negotiation of anonymous cipher suites or unexpected certificate validation failures.

Compensating Controls: Ensure that applications are configured to prefer TLS 1.3 where possible, as the TLS 1.3 implementation in Erlang/OTP is not affected by this specific logic flaw.

Public Exploit Available: No confirmed public exploit (weaponized or curated) is available in the provided data.

This vulnerability represents a significant risk to the security of all data in transit for applications using the affected Erlang/OTP versions. Organizations must prioritize updating their Erlang runtime environments and, where possible, enforce the use of TLS 1.3 to mitigate the risks associated with older, vulnerable TLS implementations.