OPNsense core: Log forgery via login username CRLF enables IP lockout bypass
Summary
The WebGUI login in OPNsense does not strip carriage-return and line-feed characters from the username field. An unauthenticated attacker with network access to the login page can inject forged authentication events into the lockout log processing. This allows blocking arbitrary IP addresses in the sshlockout PF table, including administrative, DNS or gateway addresses, or resetting the attacker's own brute-force counter.
Affected
- OPNsense core before 26.1.11
- According to the vendor advisory GHSA-2v2x-m4j7-76pv, also 26.4 up to 26.4.1 (fixed in 26.4.1p1)
Fixed in
- 26.1.11
- 26.4.1p1 (per vendor advisory)
- Unknown for 26.7.x: no fixed version confirmed in the vendor advisory
Workaround
- Unknown. No vendor-published workaround found.
- Restrict WebGUI access to management networks until patched.
Exploitation
- CISA SSVC: exploitation none, automatable no.
- No public exploit or in-the-wild exploitation known at time of research.
Our recommendation
- Upgrade to OPNsense 26.1.11 or later, or to a fixed 26.4.x or 26.7.x release; the 26.1 branch is out of security support, so upgrading to a supported branch is preferred.
- Check whether the WebGUI is reachable from WAN or untrusted networks and restrict it to management networks.
- Keep out-of-band administrative access in case forged lockouts block management addresses.
- Review the sshlockout table and the authentication logs for unexpected entries.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-2v2x-m4j7-76pv github.com
- Fix commit 8bdaad9 github.com
- Fix commit c930ab5 github.com
- OSV CVE-2026-63442 osv.dev
- OPNsense 26.1 release notes docs.opnsense.org
- endoflife.date OPNsense endoflife.date
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 19:00.
Original description (NVD)
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.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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