WeasyPrint has CSS Injection via Presentational Hints

Exploitation

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

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-49452: 0.37% estimated exploitation activity in the next 30 days; percentile 31.24 (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 A CSS injection issue exists in WeasyPrint when HTML presentational hints are enabled. Unescaped attribute values are embedded into CSS, allowing injection of arbitrary CSS declarations. This affects applications processing untrusted HTML input. Details File: weasyprint/css/init.py The background attribute is used to construct CSS: background-image:url({element.get("background")}) This string is parsed by tinycss2.parseblockscontents(). Because the value is not escaped, additional CSS declarations can be injected. PoC <body background="x);background-image:url(http://169.254.169.254/latest/meta-data/)" Impact - CSS injection - Server-side requests via injected url() - Limited to cases where presentationalhints=True Suggested Fix - Escape attribute values before embedding into CSS - Restrict allowed values for presentational hints VULN-05cssinjectionpresentationalhints.md

Published by the source

6 Jul 2026, 17:29 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jhhc-3hcp-qhm5

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jhhc-3hcp-qhm5

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# Patch Next advisory brief: CVE-2026-49452

Advisory: WeasyPrint has CSS Injection via Presentational Hints
IDs: CVE-2026-49452, GHSA-jhhc-3hcp-qhm5
Record: https://patchnext.com/advisories/cve-2026-49452 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI weasyprint: affected <= 68.1

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

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on weasyprint.
- 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-jhhc-3hcp-qhm5 (OSV record GHSA-jhhc-3hcp-qhm5 lists affected ranges: PyPI weasyprint >=0 <=68.1)
- Verified: https://github.com/advisories/GHSA-jhhc-3hcp-qhm5 (GitHub-reviewed advisory GHSA-jhhc-3hcp-qhm5 lists affected ranges: PyPI weasyprint >=0 <=68.1)

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