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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是美国Graylog公司开源的一套集中式日志管理解决方案。该产品支持捕获、存储和实时分析日志等。 Graylog 6.3.12之前版本、7.0.7之前版本和7.1.2之前版本存在输入验证错误漏洞，该漏洞源于FortiGate键值syslog解析器错误处理带引号值中的类字段文本，可能导致未经身份验证的网络发送者操纵安全日志字段或规避日志记录以掩盖恶意活动。

CVSS 7.5 · High EPSS 0.63% · P49

Possible ATT&CK Techniques 2 AI

T1604 T1070 · Indicator Removal

Affected Version Matrix 3

VendorProduct Version RangeStatus
Graylog2 graylog2-server < 6.3.12 affected
>= 7.0.0-alpha.1, < 7.0.7 affected
>= 7.1.0-alpha.1, < 7.1.2 affected
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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
Vulnerability Title
Graylog 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Graylog是美国Graylog公司开源的一套集中式日志管理解决方案。该产品支持捕获、存储和实时分析日志等。 Graylog 6.3.12之前版本、7.0.7之前版本和7.1.2之前版本存在输入验证错误漏洞，该漏洞源于FortiGate键值syslog解析器错误处理带引号值中的类字段文本，可能导致未经身份验证的网络发送者操纵安全日志字段或规避日志记录以掩盖恶意活动。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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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