CVE-2026-48859 SSH server timing side-channel in ssh_auth:check_password/3 allows unauthenticated username enumeration
Unauthenticated attackers can enumerate valid usernames via timing side-channels when the Erlang OTP SSH server uses non-default password authentication options.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-48859?
CVE-2026-48859 is a medium-severity vulnerability in Erlang OTP, published on 10 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-208
Which versions are affected by CVE-2026-48859?
It affects 2 products.
Products include Erlang Erlang\/Otp, Erlang Erlang\/Ssh.
How do I fix CVE-2026-48859?
No fix has been published for CVE-2026-48859 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-48859 being exploited?
There is no known exploitation of CVE-2026-48859 in the wild and no public exploit code.
Other vulnerabilities in Erlang OTP
- CVE-2022-37026 Auth bypass in n/a
- CVE-2016-10253 Memory corruption in n/a
- CVE-2026-55953 TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication
- CVE-2026-49759 Stack buffer overflow in SCTP error cause parsing in inet_drv allows remote VM crash
- CVE-2026-58227 TLS/DTLS denial of service via unbounded recursion on cross-signed peer certificate chain
Sources
Also known as EEF-CVE-2026-48859, GHSA-3w6p-vwhf-wvp4, UBUNTU-CVE-2026-48859.