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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.003 (16.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 17th percentile — 16.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Weakness classification (CWE)
References
- github.com/EmilStenstrom/justhtml/security/advisories/GHSA-5vp3-3cg6-2rq3 (vendor-advisory)
- www.vulncheck.com/advisories/justhtml-before-xss-via-code-fence-breakout (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.