CVE-2026-8445 justhtml before 1.12.0 Sanitizer Bypass via Markdown
An attacker can bypass HTML sanitization in justhtml by injecting raw HTML via Markdown conversion, leading to cross-site scripting when the output is rendered.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-8445?
CVE-2026-8445 is a critical cross-site scripting vulnerability in EmilStenstrom justhtml, published on 23 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-8445?
2 open source packages ship an affected version, including justhtml.
| Package | Affected | Fixed in |
|---|---|---|
justhtml PyPI | All versions | 1.12.0 |
justhtml PyPI | All versions | 1.12.0 |
How do I fix CVE-2026-8445?
Upgrade justhtml to 1.12.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-8445 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8445 exists.
Sources
Also known as GHSA-3rcm-vjrc-p45j, GHSA-wf6m-786j-gxrr.