Hydro @hydrooj/ui-default before 4.59.1 Stored XSS via Markdown language- Class

Advisories

Hydro @hydrooj/ui-default before 4.59.1 Stored XSS via Markdown language- Class

Severity: critical
Date: 11/11/2026
Affecting: @hydrooj/ui-default >= 0, < 4.59.1
CVE: CVE-2026-126800
CWE: CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVSS: 9.3
CVSS V4 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
References: https://github.com/hydro-dev/Hydro/commit/3bae56fe8edddff12346bcb1c8281269c94688d8
https://github.com/hydro-dev/Hydro/blob/3c8286dd1350fcd00412e95d5b056dbfed64edda/packages/ui-default/backendlib/markdown-it-xss.ts#L150-L157
https://vul.yulun.ac.cn/20261107/hydro/
Credit: Wu Yulun
Description: Hydro @hydrooj/ui-default before 4.59.1 contains a stored cross-site scripting vulnerability that allows registered users to inject script by placing double quotes in language- class tokens within markdown-it-xss.ts. Attackers can store a payload in their profile bio that executes when administrators or other users view it, stealing the non-httpOnly sid session cookie for session hijacking.

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