Vulnerability · Published Aug 23, 2026 · Assigned by VulnCheck

CVE-2026-8445justhtml before 1.12.0 Sanitizer Bypass via Markdown

Critical 9.8

In plain English

A critical-severity cross-site scripting in justhtml from EmilStenstrom. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical

Exploit odds (30 days)0.6%top 49.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

justhtml versions <= 1.11.0 (fixed in 1.12.0) do not sufficiently escape HTML-significant characters (angle brackets) in text nodes when converting a parsed document to Markdown via to_markdown(). While a small set of Markdown metacharacters are escaped, characters such as < and > are preserved, so untrusted input that is safe in to_html() — including entity-decoded text (e.g. <script>) or text from RCDATA/RAWTEXT-parsed elements like <title>, <textarea>, <noscript>, and <plaintext> — can be emitted as raw HTML in the Markdown output, enabling a sanitizer bypass and potential cross-site scripting when that output is rendered.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	justhtml	1.12.0	GHSA-3rcm-vjrc-p45j

Affected products (as reported)

Vendor	Product	Versions
EmilStenstrom	justhtml	0 – before 1.12.0

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

References

GitHub Security Advisory (GHSA-3rcm-vjrc-p45j) vendor-advisory
VulnCheck Advisory: justhtml before 1.12.0 Sanitizer Bypass via Markdown third-party-advisory