CVE-2026-5389justhtml before 1.13.0 XSS via code fence breakout
Updated under an hour ago ()
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It affects EmilStenstrom justhtml. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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justhtml versions before 1.13.0 contain a cross-site scripting vulnerability in the to_markdown() function when serializing attacker-controlled pre content. Attackers can place backticks inside sanitized pre elements to break out of fixed-length code fences, allowing raw HTML to execute when the generated Markdown is rendered by CommonMark or GFM-style renderers.
- CVSS
- 6.1 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Weakness (CWE)
- CWE-80
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- VulnCheck
- NVD analysis
- Deferred
- Record last updated
- Aug 24, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
EmilStenstrom justhtml emilstenstrom:justhtml (from the name) | before 1.13.0; 1.13.0 not affected | CNA record |
References
- https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-5vp3-3cg6-2rq3vendor-advisory
- https://www.vulncheck.com/advisories/justhtml-before-xss-via-code-fence-breakoutthird-party-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.