This vulnerability in Erlang/OTP SSH (ssh_auth and ssh_options modules) allows unauthenticated remote attackers to enumerate valid usernames via a timing side-channel during password authentication. When the SSH daemon is configured with the user_passwords or password options, ssh_auth:check_password/3 performs a PBKDF2-SHA256 computation with 600,000 iterations (~300ms) for valid usernames but returns immediately (~0ms) for invalid usernames. This timing difference is detectable in a single authentication attempt, enabling username enumeration. The affected versions are OTP 29.0 up to but not including 29.0.2 and SSH 6.0 up to but not including 6.0.1. The user_passwords and password options are intended for test purposes; the recommended alternative is pwdfun, which is not vulnerable. No official fix or patch is currently documented.

An unauthenticated remote attacker can distinguish valid usernames from invalid ones by measuring the response time during SSH password authentication attempts. This can facilitate further targeted attacks such as brute force or social engineering. The vulnerability does not allow direct password compromise or code execution but leaks information about valid user accounts.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vendor recommends avoiding the use of the user_passwords and password options in production environments and instead using the pwdfun option, which is not affected by this vulnerability. Until an official fix is released, disabling or not using the vulnerable options is the primary mitigation.