Sources: National Vulnerability Database, CVE.org, CISA KEV, FIRST EPSS
CVE-2026-126800 Overview
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.
Critical Impact
Affected Products
- Hydro @hydrooj/ui-default: see the vendor advisory for the exact affected versions
Discovery Timeline
- 2026-11-11: CVE-2026-126800 published to the National Vulnerability Database by disclosure@vulncheck.com
- 2026-11-11: last updated in the NVD database
Technical Details for CVE-2026-126800
Vulnerability Analysis
CVE-2026-126800 is a Cross Site Scripting weakness (CWE-79: Cross Site Scripting) in Hydro @hydrooj/ui-default. Based on its CVSS vector, the flaw can be reached over the network, needs some level of access, and relies on a user taking an action. Attacker supplied script runs in another user's browser inside the trusted site.
With a CVSS base score of 9.3, apply the vendor fix and confirm exposure on internet facing and business critical assets first.
Root Cause
The weakness is classified as CWE-79: Cross Site Scripting. Attacker supplied script runs in another user's browser inside the trusted site.
Attack Vector
Based on the CVSS vector, the flaw can be reached over the network, needs some level of access, and relies on a user taking an action. Attack complexity is low complexity.
No exploitation in the wild is confirmed by CISA at the time of the last update. Check the references below for any vendor or researcher proof of concept.
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Detection Methods for CVE-2026-126800
Detection Strategies
- Inventory every instance of Hydro @hydrooj/ui-default and compare the running version with the affected range above.
- Check external attack surface scans for internet facing instances of the component.
- Run an authenticated vulnerability scan once your scanner ships a check for this CVE.
Monitoring Recommendations
- Forward Hydro @hydrooj/ui-default application, access and audit logs to your SIEM for retrospective hunting.
- Alert on new processes, configuration changes or outbound connections from the affected service.
- Track the vendor advisory and the CISA KEV catalog for changes in exploitation status.
How to Mitigate CVE-2026-126800
Immediate Actions Required
- Apply the fixed version of Hydro @hydrooj/ui-default named in the vendor advisory.
- Prioritize internet facing and business critical instances first.
- Rescan after the change to confirm the exposure is closed.
Patch Information
Use the fixed version listed in the vendor advisory for Hydro @hydrooj/ui-default.
Workarounds
- If patching must wait, restrict network access to the affected service and place it behind authentication or a web application firewall rule.
CWE References
- CWE-79: Cross Site Scripting More CVEs with this weakness
Technical References
This entry is built directly from NVD, CISA KEV and EPSS data. Verify fixed versions in the vendor advisory before you deploy.
Frequently asked questions
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