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CVE-2026-126800 Hydro @hydrooj/ui-default before 4.59.1 Stored XSS via Markdown language- Class

9.3 criticalEPSS 0.3%

Critical (9.3) in hydro-dev @hydrooj/ui-default. EPSS 0.3% estimated probability of exploitation activity in the next 30 days.

On this page
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.

Severity

CVSS 4.0

9.3 critical
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

CVSS 3.1

8.7 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
EPSS
0.3% estimated probability of exploitation activity in the next 30 days; 24th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: total, assessed 2026-11-12. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
CWE
CWE-79 Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
OWASP Top 10
A05:2025 Injection
Published
Modified
Assigned by
VulnCheck (CNA)
NVD analysis
Deferred: the NVD does not plan to analyze it
Record from
the NVD, synced

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CVE-2026-126800

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Affected

  • hydro-dev:@hydrooj/ui-default

Versions

From the CNA's record in the CVE List.

ProductAffected
hydro-dev @hydrooj/ui-defaultbefore 4.59.1

Attack patterns (CAPEC)

  • CAPEC-63 Cross-Site Scripting (XSS) Likelihood: High · Severity: Very High
  • CAPEC-85 AJAX Footprinting Likelihood: High · Severity: Low
  • CAPEC-209 XSS Using MIME Type Mismatch Severity: Medium
  • CAPEC-588 DOM-Based XSS Likelihood: High · Severity: Very High
  • CAPEC-591 Reflected XSS Likelihood: High · Severity: Very High
  • CAPEC-592 Stored XSS Likelihood: High · Severity: Very High

The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.

History

  1. The NVD deferred its analysis

Changes since this site first stored the record. The same for every record: /api/public/changes.

References

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