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High, CVSS 7.5amended

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

CVE-2026-55841GHSA-gqr6-r77p-c2pj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (org.graylog2:graylog2-server 7.1.2, 7.0.7, 6.3.12), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS
  • CVE-2026-55841: 0.63% estimated exploitation activity in the next 30 days; percentile 50.40 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact 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. Patches 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. 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. [^1]:…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-gqr6-r77p-c2pj

  2. Revision 1 · created ·

    Published from osv record GHSA-gqr6-r77p-c2pj

Agent brief

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# Patch Next advisory brief: CVE-2026-55841

Advisory: Fortigate syslog message parser can be exploited to modify or delete fields from the original message
IDs: CVE-2026-55841, GHSA-gqr6-r77p-c2pj
Record: https://patchnext.com/advisories/cve-2026-55841 (revision 2, source checked 26 Oct 2026, 16:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.graylog2:graylog2-server 7.1.2, 7.0.7, 6.3.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.graylog2:graylog2-server: affected < 6.3.12; >= 7.0.0, < 7.0.7; >= 7.1.0, < 7.1.2; fixed in 6.3.12, 7.0.7, 7.1.2

## Suggested inspection (read-only)
- Maven org.graylog2:graylog2-server: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.graylog2:graylog2-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gqr6-r77p-c2pj (OSV record GHSA-gqr6-r77p-c2pj lists affected ranges: Maven org.graylog2:graylog2-server >=0 =7.0.0 =7.1.0 <7.1.2 (fixed))
- Verified: https://github.com/advisories/GHSA-gqr6-r77p-c2pj (GitHub-reviewed advisory GHSA-gqr6-r77p-c2pj lists affected ranges: Maven org.graylog2:graylog2-server >=0 =7.0.0 =7.1.0 <7.1.2)

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