CVE-2026-55841 Graylog: Fortigate syslog message parser can be exploited to modify or delete fields from the original message
An unauthenticated attacker can manipulate or delete security log fields via crafted syslog messages, potentially evading detection in Graylog.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55841?
CVE-2026-55841 is a high-severity vulnerability in graylog2-server, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Graylog is a free and open log management platform. Prior to Graylog Server versions 6.3.12, 7.0.7, and 7.1.2 and Graylog Forwarder version 7.3, the FortiGate key-value syslog parser in graylog2-server/src/main/java/org/graylog2/inputs/codecs/GLFortiGateSyslogEvent.java and graylog2-server/src/main/java/org/graylog2/inputs/codecs/SyslogCodec.java mishandles field-like text inside quoted values. GLFortiGateSyslogEvent.getFields() uses KV_PATTERN and QUOTED_KV_PATTERN, while SyslogCodec.parse() invokes the FortiGateSyslogEvent parser; crafted values containing = or backslash-escaped quotes can cause embedded keys such as srcip, dstip, date, time, and tz to remove or overwrite original top-level fields or produce an invalid message that Graylog discards. An unauthenticated network sender who can submit syslog messages can therefore manipulate security-log fields or evade logging to obscure malicious activity. This issue is fixed in Graylog Server versions 6.3.12, 7.0.7, and 7.1.2 and Graylog Forwarder version 7.3.
Weakness: CWE-138
Which versions are affected by CVE-2026-55841?
6 open source packages ship an affected version, including org.graylog2:graylog2-server.
| Package | Affected | Fixed in |
|---|---|---|
org.graylog2:graylog2-server Maven | All versions | 6.3.12 |
org.graylog2:graylog2-server Maven | All versions | 6.3.12 |
org.graylog2:graylog2-server Maven | From 7.0.0 | 7.0.7 |
org.graylog2:graylog2-server Maven | From 7.0.0 | 7.0.7 |
org.graylog2:graylog2-server Maven | From 7.1.0 | 7.1.2 |
org.graylog2:graylog2-server Maven | From 7.1.0 | 7.1.2 |
How do I fix CVE-2026-55841?
Upgrade org.graylog2:graylog2-server to a fixed version for your release line: 6.3.12, 7.0.7 or 7.1.2.
Is CVE-2026-55841 being exploited?
There is no known exploitation of CVE-2026-55841 in the wild and no public exploit code.
Sources
Also known as GHSA-gqr6-r77p-c2pj.