Vulnerability · Published Aug 23, 2026 · Assigned by VulnCheck

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

Medium 6.1

In plain English

A medium-severity cross-site scripting in justhtml from EmilStenstrom. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.3%top 81.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	justhtml	1.22.0	GHSA-jf6w-2mvx-633j

Affected products (as reported)

Vendor	Product	Versions
EmilStenstrom	justhtml	0.9.0 – through 1.21.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References

GitHub Security Advisory (GHSA-jf6w-2mvx-633j) vendor-advisory
VulnCheck Advisory: justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span third-party-advisory