A critical vulnerability in the coturn TURN and STUN server allows remote attackers to predict security nonces and relay ports, potentially facilitating unauthorized relay access.

The software utilizes a weak pseudo-random number generator for nonces and port randomization rather than cryptographically secure alternatives. By observing a sequence of unauthenticated allocation requests, an attacker can reconstruct the state of the generator, enabling them to predict future nonces and relay ports.

The ability to predict nonces and relay ports undermines the authentication integrity of the TURN/STUN server. This could allow unauthorized parties to relay traffic through the server, potentially bypassing network access controls or obfuscating malicious activities. Given the CVSS score of 7.7, this represents a significant risk to the confidentiality and integrity of communications relay infrastructure.

Immediate Action: Update the coturn implementation to a version containing the fix, specifically incorporating commit 11fc465f4bba70bb0ad8aae17d6c4a63a29917d9 or later releases.

Proactive Monitoring: Monitor server logs for an unusual volume of unauthenticated allocation requests from single or distributed IP addresses, which may indicate an attempt to reconstruct the PRNG state.

Compensating Controls: Restrict access to the TURN/STUN server to known, trusted IP ranges where possible to limit the ability of external actors to perform the required sequence of requests for state reconstruction.

Public Exploit Available: Unknown

This vulnerability presents a clear risk to the security of relay services by allowing predictable authentication tokens. Organizations utilizing coturn must prioritize upgrading to the patched version immediately to ensure that nonces and relay ports are generated with cryptographically secure randomness. Failure to patch may expose the relay infrastructure to unauthorized use and traffic manipulation.