JustHTML has a Sanitizer Bypass (in Markdown)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-8445: 0.64% estimated exploitation activity in the next 30 days; percentile 50.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary tomarkdown() does not sufficiently escape text content that looks like HTML. As a result, untrusted input that is safe in tohtml() can become raw HTML in Markdown output. This is not specific to tokenizer raw-text states like <title, <noscript, or <plaintext, although those states can trigger the behavior. The root cause is broader: Markdown text serialization leaves angle brackets unescaped in text nodes. Details When converting a parsed document to Markdown, text nodes are escaped for a small set of Markdown metacharacters, but HTML-significant characters such as < and are preserved. That means content parsed as text, including entity-decoded text or text produced by RCDATA/RAWTEXT-style parsing, can be emitted into Markdown as raw HTML. Examples of affected input include: - Text produced from entity-decoded input such as &lt;script&gt;...&lt;/script&gt; - Text inside elements like <title, <textarea, <noscript (when parsed as raw text), and <plaintext This is distinct from…

Published by the source

18 Mar 2026, 20:19 UTC

Last modified by the source

24 Aug 2026, 03:56 UTC

Source last checked

26 Oct 2026, 13:37 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3rcm-vjrc-p45j

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3rcm-vjrc-p45j

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# Patch Next advisory brief: CVE-2026-8445

Advisory: JustHTML has a Sanitizer Bypass (in Markdown)
IDs: CVE-2026-8445, GHSA-3rcm-vjrc-p45j
Record: https://patchnext.com/advisories/cve-2026-8445 (revision 3, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: justhtml 1.12.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI justhtml: affected <= 1.11.0; fixed in 1.12.0

## Suggested inspection (read-only)
- `python -m pip show justhtml`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on justhtml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3rcm-vjrc-p45j (OSV record GHSA-3rcm-vjrc-p45j lists affected ranges: PyPI justhtml >=0 <1.12.0 (fixed))
- Verified: https://github.com/advisories/GHSA-3rcm-vjrc-p45j (GitHub-reviewed advisory GHSA-3rcm-vjrc-p45j lists affected ranges: PyPI justhtml >=0 <=1.11.0)

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