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CVE-2026-41887— Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)

Quick assessment

Affected
flarum framework
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.

Flarum是Flarum开源的一个用于构建社区的简单论坛软件。 Flarum 1.8.16之前版本和2.0.0-rc.1之前版本存在路径遍历漏洞，该漏洞源于对LESS配置变量值未进行限制，可能导致任意文件包含或服务端请求伪造。

CVSS 4.9 · Medium EPSS 0.46% · P38

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
flarum framework < 1.8.16 affected
>= 2.0.0-beta.1, < 2.0.0-rc.1 affected
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I. Basic Information for CVE-2026-41887

Vulnerability Information
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Vulnerability Title
Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)
Source: CVE Program / CVE List V5
Vulnerability Description
Flarum is open-source forum software. Prior to versions 1.8.16 and 2.0.0-rc.1, Flarum's patch for CVE-2023-27577 restricted the @import and data-uri() LESS features in the custom_less setting, but the same restriction was never applied to other settings registered as LESS config variables (for example theme_primary_color and theme_secondary_color, as well as any key registered via Extend\Settings::registerLessConfigVar()). Those values are interpolated verbatim into the LESS source at compile time, allowing an authenticated administrator to craft a theme-color value that injects an arbitrary @import directive into the compiled forum.css. Because the underlying LESS parser honours @import (inline) '<path>', an attacker can read arbitrary files reachable by the PHP process (local file inclusion) or trigger outbound HTTP(S) requests (server-side request forgery). This issue has been patched in versions 1.8.16 and 2.0.0-rc.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5
Vulnerability Title
Flarum 路径遍历漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Flarum是Flarum开源的一个用于构建社区的简单论坛软件。 Flarum 1.8.16之前版本和2.0.0-rc.1之前版本存在路径遍历漏洞，该漏洞源于对LESS配置变量值未进行限制，可能导致任意文件包含或服务端请求伪造。
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
flarum framework < 1.8.16 -

II. Public POCs for CVE-2026-41887

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III. Intelligence Information for CVE-2026-41887

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Patches & Fixes for CVE-2026-41887 (2)

Vendor Advisories for CVE-2026-41887 (1)

Vendor Pages for CVE-2026-41887 (1)

IV. Related Vulnerabilities

Same product: framework
Same vendor: flarum
Same weakness: CWE-22

V. Comments for CVE-2026-41887

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