JustHTML Affected by Mutation XSS via Literal Text Serialization in Raw Text Elements (style/script)

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-2026-8630: 0.26% estimated exploitation activity in the next 30 days; percentile 18.16 (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 Sanitized DOM trees can be unsafe to serialize when a custom policy allows raw-text elements such as <style or <script. The issue affects DOM trees that are constructed or modified programmatically and then passed through sanitizedom() with a policy that keeps these elements. Text nodes inside <style and <script are serialized literally, so attacker-controlled text containing the matching closing tag sequence can break out of the raw-text context and inject HTML into the serialized output. The default sanitization policy is not affected because it drops the contents of style and script. Details The root cause is in HTML serialization of raw-text elements. In serialize.py, text children of script and style are emitted verbatim: python LITERALTEXTSERIALIZATIONELEMENTS = frozenset({"script", "style"}) def serializetextforparent(text: str | None, parentname: str | None) - str: if not text: return "" if parentname in LITERALTEXTSERIALIZATIONELEMENTS: return text return…

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-qvc2-mg72-jjhx

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-qvc2-mg72-jjhx

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# Patch Next advisory brief: CVE-2026-8630

Advisory: JustHTML Affected by Mutation XSS via Literal Text Serialization in Raw Text Elements (style/script)
IDs: CVE-2026-8630, GHSA-qvc2-mg72-jjhx
Record: https://patchnext.com/advisories/cve-2026-8630 (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-qvc2-mg72-jjhx (OSV record GHSA-qvc2-mg72-jjhx lists affected ranges: PyPI justhtml >=0 <1.12.0 (fixed))
- Verified: https://github.com/advisories/GHSA-qvc2-mg72-jjhx (GitHub-reviewed advisory GHSA-qvc2-mg72-jjhx lists affected ranges: PyPI justhtml >=0 <=1.11.0)

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