CVE-2026-5389

MEDIUM 6.1

justhtml before 1.13.0 XSS via code fence breakout

CVSS Score

6.1

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-80
Vendor	emilstenstrom
Product	justhtml
Published	Aug 23, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

EmilStenstrom / justhtml

0 < 1.13.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-5vp3-3cg6-2rq3 vulncheck.com: https://www.vulncheck.com/advisories/justhtml-before-xss-via-code-fence-breakout

Credits

🔍 AlfinJ0se