OPNsense: Log Forgery via Login Username CRLF in WebGUI Authentication → Pf Table IP Blocking

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

OPNsense is a FreeBSD based firewall and routing platform. Prior to version 26.1.11, the unauthenticated WebGUI login usernamefld accepts carriage-return and line-feed characters that survive LOG_AUTH processing through syslog-ng-lockout.conf into the syslog-ng program destination feeding lockout_handler. The consumer's readline() processing treats an injected fragment as a separate authentication event and selects the first syntactically valid IP address from the forged line. An attacker with network access to the login page can forge failure events for another IP, causing that IP to be added to the sshlockout PF table and its active states to be killed, or forge accepted events that reset an attacker's own brute-force counter. This can block administrative, DNS, gateway, or monitoring addresses and can bypass password-guessing lockout without authentication. This issue is fixed in version 26.1.11.

Source published

15 Oct 2026 15:22:16 UTC

Source modified

16 Oct 2026 17:13:35 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

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CVSS 3.1 · 8.1 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H