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.
No advisories yet.
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.
Wed, 10 Jun 2026 17:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
|
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
|
Projects
Sign in to view the affected projects.
Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-06-10T16:19:43.145Z
Reserved: 2026-05-25T20:44:10.697Z
Link: CVE-2026-48859
Updated: 2026-06-10T16:19:38.063Z
Status : Received
Published: 2026-06-10T16:17:12.373
Modified: 2026-06-10T16:17:12.373
Link: CVE-2026-48859
No data.
OpenCVE Enrichment
Updated: 2026-06-10T18:00:15Z