CVE-2026-5389 MEDIUM

CVE-2026-5389: justhtml before 1.13.0 XSS via code fence breakout

Vendor Emilstenstrom

Product justhtml

Weakness CWE-80 · XSS · basic

Published August 23, 2026

Last update August 23, 2026

View on NVD All CVEs

CVSS base score

5.1/10

Attack vector Network

Attack complexity Low

Privileges required None

User interaction —

Confidentiality —

Integrity —

CVSS 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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

August 23, 2026 CVE published

External resources

03References

NVD — National Vulnerability Database https://nvd.nist.gov/vuln/detail/CVE-2026-5389 CWE — Common Weakness Enumeration https://cwe.mitre.org/data/definitions/80.html AskarLabs — CWE-80 write-up Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

Related vulnerabilities

CVE-2026-5389: justhtml before 1.13.0 XSS via code fence breakout

01Description

02Disclosure timeline

03References

04Related CVE