XSS in Emilstenstrom Justhtml
CVE-2026-77088
justhtml versions 0.9.0 through 1.21.0 contain a cross-site scripting vulnerability in to_markdown() where inline code spans fail to account for blank lines as block boundaries. Attackers can inject blank lines into code or pre element text to break the inline span, causing sanitized HTML to be emitted unescaped and re-parsed as live Markdown by compliant renderers.
Vulnerability class: XSS (Cross-Site Scripting)
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
Affected products
Weakness classification (CWE)
References
- github.com/EmilStenstrom/justhtml/security/advisories/GHSA-jf6w-2mvx-633j (vendor-advisory)
- www.vulncheck.com/advisories/justhtml-through-cross-site-scripting-via-code-span (third-party-advisory)
Frequently asked questions
- What is CVE-2026-77088?
- CVE-2026-77088 is a medium-severity vulnerability in Emilstenstrom Justhtml, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-08-23.
- How severe is CVE-2026-77088?
- Medium severity. CVSS v3 base score is 6.1 out of 10.