CVE-2026-109786

In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on <token>" suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as "x VICTIM-SOURCE-IP-ADDRESS on" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

0.3% chance of exploitation in the next 30 days; higher than 24% of CVEs (scores of 2026-10-25)

CWE

CWE-117

Published

2026-10-13

Modified

2026-10-16

Record from

the NVD, synced 2026-10-19

References

• https://coredump.ws/repos/mail-hardening.git/
• https://github.com/fail2ban/fail2ban/commit/ddd879d22664904ace24e1255ac6571808c58187

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