CVE-2026-5389

justhtml before 1.13.0 XSS via code fence breakout

Published Aug 23, 2026 CVSS 4.0 · 5.1 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Emilstenstrom
Emilstenstrom justhtml
Vendors & Products Emilstenstrom
Emilstenstrom justhtml
Type Values Removed Values Added
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.
Title justhtml before 1.13.0 XSS via code fence breakout
Weaknesses CWE-80
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}

cvssV4_0

{'score': 5.1, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Aug 24, 2026, 6:15 PM
Reserved
Apr 1, 2026, 9:14 PM
Status
Deferred
Published
Aug 23, 2026, 2:16 PM
Modified
Oct 12, 2026, 4:10 PM