What is CVE-2026-5389?

CVE-2026-5389 is a medium-severity vulnerability, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 6.1/10. Published 2026-08-23.

How severe is CVE-2026-5389?

Medium severity. CVSS v3 base score is 6.1 out of 10.

CVE-2026-5389

CVE-2026-5389

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 v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

Weakness classification (CWE)

CWE-80 — Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-5389?: CVE-2026-5389 is a medium-severity vulnerability, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 6.1/10. Published 2026-08-23.
How severe is CVE-2026-5389?: Medium severity. CVSS v3 base score is 6.1 out of 10.