CVE-2026-55841: Graylog syslog parser field injection in key-value message handling

CVE-2026-55841 · Severity: high · CVSS 7.5 · Published 2026-08-28

Graylog is a centralized log management and analysis platform used to collect and parse syslog messages from network devices like Fortigate firewalls. A parsing vulnerability allows attackers to inject specially crafted messages that modify or delete fields from legitimate log records, or cause Graylog to discard messages entirely. This breaks the integrity of security logs and enables attackers to hide their activity from audit trails and security investigations.

Technologies: Graylog, org.graylog2:graylog2-server (Maven). Vendors: Graylog, Maven.

Quick answers

Is CVE-2026-55841 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55841 being exploited in the wild.
How severe is CVE-2026-55841?
High severity, with a CVSS score of 7.5, published 28 August 2026.
Which products and versions are affected?
Graylog < 6.3.12, >= 7.0.0 and < 7.0.7, >= 7.1.0 and < 7.1.2; org.graylog2:graylog2-server (Maven) ECOSYSTEM:introduced=0,fixed=6.3.12.
Is there a fix for CVE-2026-55841?
Yes. org.graylog2:graylog2-server (Maven): upgrade to 6.3.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55841 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-55841?
Check whether you run Graylog or org.graylog2:graylog2-server (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • org.graylog2:graylog2-server (Maven): upgrade to 6.3.12 or later
    # set org.graylog2:graylog2-server to 6.3.12 in your pom.xml or build.gradle

Technical details

The vulnerability is a special-element injection flaw (CWE-138) in Graylog's parsing logic for key-value syslog messages originating from Fortigate devices. When processing these messages, the parser fails to properly neutralize or escape special control elements, allowing an attacker to inject additional key-value pairs that overwrite legitimate message fields. Alternatively, attackers can craft invalid payloads that cause Graylog to reject and discard the entire message. The attack is network-accessible and requires no authentication or user interaction. An unauthenticated attacker on the network with the ability to send syslog messages to Graylog (or via a Fortigate device) can exploit this to tamper with or delete audit logs, facilitating log evasion. Patches are available in versions 6.3.12, 7.0.7, and 7.1.2.

Affected products

  • Graylog graylog2-server < 6.3.12, >= 7.0.0 and < 7.0.7, >= 7.1.0 and < 7.1.2

Identifiers

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

Timeline

  • 2026-06-24: disclosed: Vulnerability disclosed to Graylog
  • 2026-08-28: advisory: Advisory published (GHSA-gqr6-r77p-c2pj, CVE-2026-55841)
  • 2026-06-24: patched: Patches released in versions 6.3.12, 7.0.7, 7.1.2

References

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