CVE-2026-5389
justhtml before 1.13.0 XSS via code fence breakout
- State
- Published
- Severity
- 5.1 Medium
- Published
- Aug 23, 2026
- Updated
- Aug 24, 2026
- Reserved
- Apr 1, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 5.1 Medium | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N | VulnCheck |
| 3.1 | 6.1 Medium | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N | VulnCheck |
Weaknesses
- CWE-80 Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
Affected Products
| Product | Versions |
|---|---|
justhtmlEmilStenstrom |
|
References
- GitHub Security Advisory (GHSA-5vp3-3cg6-2rq3)vendor-advisory
- VulnCheck Advisory: justhtml before 1.13.0 XSS via code fence breakoutthird-party-advisory
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