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 29.0.2 corresponding to ssh from 6.0 before 6.0.1.

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Fixes

Solution

No solution given by the vendor.


Workaround

Use the pwdfun option instead of user_passwords for password authentication. The pwdfun callback gives full control over timing behavior and is not affected by this vulnerability. Implementations should take care to execute in approximately constant time regardless of username validity.

History

Wed, 10 Jun 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 10 Jun 2026 16:00:00 +0000

Type Values Removed Values Added
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 29.0.2 corresponding to ssh from 6.0 before 6.0.1.
Title SSH server timing side-channel in ssh_auth:check_password/3 allows unauthenticated username enumeration
First Time appeared Erlang
Erlang erlang\/otp
Weaknesses CWE-208
CPEs cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
Vendors & Products Erlang
Erlang erlang\/otp
References
Metrics cvssV4_0

{'score': 6.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-06-10T16:19:43.145Z

Reserved: 2026-05-25T20:44:10.697Z

Link: CVE-2026-48859

cve-icon Vulnrichment

Updated: 2026-06-10T16:19:38.063Z

cve-icon NVD

Status : Received

Published: 2026-06-10T16:17:12.373

Modified: 2026-06-10T16:17:12.373

Link: CVE-2026-48859

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses