CVE-2026-77088: justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-23 · updated 2026-10-12
Weakness: CWE-79

Description

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.

Affected products

EmilStenstrom justhtml: from 0.9.0 through 1.21.0

References

https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-jf6w-2mvx-633j
https://www.vulncheck.com/advisories/justhtml-through-cross-site-scripting-via-code-span

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