{"id":"EEF-CVE-2026-48859","summary":"SSH server timing side-channel in ssh_auth:check_password/3 allows unauthenticated username enumeration","details":"## Summary\n\nObservable Timing Discrepancy vulnerability in Erlang/OTP ssh (ssh_auth, ssh_options modules) allows unauthenticated remote username enumeration via timing side-channel in password authentication.\n\nWhen 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.\n\nThe `user_passwords` and `password` options are documented as intended for test purposes; the recommended alternative is `pwdfun`, which is not affected by this vulnerability.\n\nThis vulnerability is associated with program files `lib/ssh/src/ssh_auth.erl` and `lib/ssh/src/ssh_options.erl`.\n\nThis issue affects OTP from OTP 29.0 before OTP 29.0.2, corresponding to ssh from 6.0 before 6.0.1.\n\n## Workarounds\n\n* 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.\n* Restrict SSH port access to trusted networks only via firewall rules, reducing the set of potential attackers who can perform timing measurements.\n\n## Configurations\n\nThe SSH daemon must be configured with the `user_passwords` or `password` option for password authentication. Systems using the `pwdfun` option instead are not affected.","aliases":["CVE-2026-48859","GHSA-3w6p-vwhf-wvp4"],"modified":"2026-09-08T01:15:05.843165550Z","published":"2026-06-10T14:35:43.553Z","database_specific":{"cwe_ids":["CWE-208"],"capec_ids":["CAPEC-116"],"cpe_ids":["cpe:2.3:a:erlang:erlang\\/otp:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/erlang/otp/security/advisories/GHSA-3w6p-vwhf-wvp4"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-48859.html"},{"type":"WEB","url":"https://www.erlang.org/doc/system/versions.html#order-of-versions"},{"type":"FIX","url":"https://github.com/erlang/otp/commit/c342092ef4b369bb409d5b71ac8fd83bab74aedf"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/erlang/otp","events":[{"introduced":"032d1bc9491a3975c68faf9bc7776115d6ae3005"},{"fixed":"c342092ef4b369bb409d5b71ac8fd83bab74aedf"}]}],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-48859.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"Zhang Delong","type":"FINDER"},{"name":"Jakub Witczak","type":"REMEDIATION_DEVELOPER"},{"name":"Ingela Anderton Andin","type":"REMEDIATION_REVIEWER"},{"name":"Michał Wąsowski","type":"REMEDIATION_REVIEWER"}]}