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CVE-2026-55841— Graylog: Fortigate syslog message parser can be exploited to modify or delete fields from the original message

Quick assessment

Affected
Graylog2 graylog2-server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Graylog 是一个免费且开源的日志管理平台。在 Graylog Server 6.3.12、7.0.7 和 7.1.2 之前，以及 Graylog Forwarder 7.3 之前的版本中，位于 和 中的 FortiGate 键值（key-value）syslog 解析器在处理引号内类字段文本时存在缺陷。 使用了 和 ，而 会调用 FortiGateSyslogEvent 解析器；经过精心构造的包含等号 或反斜杠转义引号的值，可能导致嵌入的键（如 、 、 、 、 ）删除或覆盖原始顶层字段，或者生成无效的日志消息

CVSS 7.5 · High

Possible ATT&CK Techniques 2 AI

T1604 T1070 · Indicator Removal
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I. Basic Information for CVE-2026-55841

Vulnerability Information
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Vulnerability Title
Graylog: Fortigate syslog message parser can be exploited to modify or delete fields from the original message
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对特殊元素的转义处理不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Graylog2 graylog2-server < 6.3.12 -

II. Public POCs for CVE-2026-55841

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III. Intelligence Information for CVE-2026-55841

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Patches & Fixes for CVE-2026-55841 (7)

Vendor Advisories for CVE-2026-55841 (1)

Same Patch Batch · Graylog2 · 2026-08-28 · 3 CVEs total

CVE-2026-55867 5.3 MEDIUM Graylog token revocation endpoint allows authenticated users to delete other users’ access
CVE-2026-55425 5.0 MEDIUM Graylog: System Catalog titles endpoint can be used to retrieve values of protected databa

IV. Related Vulnerabilities

Same product: graylog2-server
Same vendor: Graylog2
Same weakness: CWE-138

V. Comments for CVE-2026-55841

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