Riskcovery

CVE-2026-48859

SSH server timing side-channel in ssh_auth:check_password/3 allows unauthenticated username enumeration

State
Published
Severity
6.3 Medium
Published
Jun 10, 2026
Updated
Sep 8, 2026
Reserved
May 25, 2026

Read the record on cve.org

Description

Observable Timing Discrepancy vulnerability in Erlang/OTP ssh (ssh_auth, ssh_options modules) allows unauthenticated remote username enumeration via timing side-channel in password authentication.

When the SSH daemon is configured with the user_passwords or password option, 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 via the ssh_options:get_password_option/2 path. This timing difference is detectable in a single authentication attempt and allows an unauthenticated attacker to distinguish valid from invalid usernames.

The user_passwords and password options are documented as intended for test purposes; the recommended alternative is pwdfun, which is not affected by this vulnerability.

This vulnerability is associated with program files lib/ssh/src/ssh_auth.erl and lib/ssh/src/ssh_options.erl.

This issue affects OTP from OTP 29.0 before OTP 29.0.2, corresponding to ssh from 6.0 before 6.0.1.

Scores

CVSSScoreVectorSource
4.06.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:NEEF

Weaknesses

  • CWE-208 Observable Timing Discrepancy

Affected Products

ProductVersions
OTPErlang
  • 29.0 to before 29.0.2Affected
OTPErlang
  • 6.0 to before 6.0.1Affected
OTPErlang
  • 032d1bc9491a3975c68faf9bc7776115d6ae3005 to before c342092ef4b369bb409d5b71ac8fd83bab74aedfAffected

References

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