CVE-2026-55841

Fortigate syslog message parser can be exploited to modify or delete fields from the original message

Workarounds

There are no feasible workarounds for this issue. Upgrading to a patched version is recommended.

To find potentially discarded messages due to parsing errors, customers of Graylog Enterprise or Security can check the Indexing and Processing Failures Index^1.

Credits

Thanks to Jose Luis González, from Fundación Sarenet, with additional analysis by Borja Marcos from Sarenet.

A security issue has been identified in Graylog affecting the parsing of syslog messages that use a key-value format, such as those generated by Fortigate devices.

The vulnerability allows attackers to overwrite individual message fields, or to produce invalid messages which Graylog will discard. This effectively enables log evasion techniques to obscure malicious activity.

CVE-2026-55841 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.3.12, 7.0.7, 7.1.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The issue has been fixed in the following Graylog versions: 6.3.12, 7.0.7, 7.1.2. Users should upgrade to one of these versions or above to remediate the vulnerability.

Graylog Cloud has already been patched.

1. What is CVE-2026-55841? CVE-2026-55841 is a high-severity security vulnerability in org.graylog2:graylog2-server (maven), affecting versions < 6.3.12. It is fixed in 6.3.12, 7.0.7, 7.1.2.
2. How severe is CVE-2026-55841? CVE-2026-55841 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of org.graylog2:graylog2-server are affected by CVE-2026-55841? org.graylog2:graylog2-server (maven) versions < 6.3.12 is affected.
4. Is there a fix for CVE-2026-55841? Yes. CVE-2026-55841 is fixed in 6.3.12, 7.0.7, 7.1.2. Upgrade to this version or later.
5. Is CVE-2026-55841 exploitable, and should I be worried? Whether CVE-2026-55841 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55841 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55841?
   • Upgrade org.graylog2:graylog2-server to 6.3.12 or later
   • Upgrade org.graylog2:graylog2-server to 7.0.7 or later
   • Upgrade org.graylog2:graylog2-server to 7.1.2 or later

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