Cross-site scripting in Bleach

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2021-23980: 0.48% estimated exploitation activity in the next 30 days; percentile 41.65 (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.

Impact A mutation XSS affects users calling bleach.clean with all of: svg or math in the allowed tags p or br in allowed tags style, title, noscript, script, textarea, noframes, iframe, or xmp in allowed tags the keyword argument stripcomments=False Note: none of the above tags are in the default allowed tags and stripcomments defaults to True. Patches Users are encouraged to upgrade to bleach v3.3.0 or greater. Note: bleach v3.3.0 introduces a breaking change to escape HTML comments by default. Workarounds modify bleach.clean calls to at least one of: not allow the style, title, noscript, script, textarea, noframes, iframe, or xmp tag not allow svg or math tags not allow p or br tags set stripcomments=True A strong Content-Security-Policy without unsafe-inline and unsafe-eval script-srcs) will also help mitigate the risk. References https://bugzilla.mozilla.org/showbug.cgi?id=1689399 https://advisory.checkmarx.net/advisory/CX-2021-4303…

Published by the source

2 Feb 2021, 17:58 UTC

Last modified by the source

8 Jul 2026, 06:27 UTC

Source last checked

26 Oct 2026, 13:16 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vv2x-vrpj-qqpq

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-vv2x-vrpj-qqpq

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# Patch Next advisory brief: CVE-2021-23980

Advisory: Cross-site scripting in Bleach
IDs: CVE-2021-23980, GHSA-vv2x-vrpj-qqpq
Record: https://patchnext.com/advisories/cve-2021-23980 (revision 3, source checked 26 Oct 2026, 13:16 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: bleach 3.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI bleach: affected < 3.3.0; fixed in 3.3.0

## Suggested inspection (read-only)
- `python -m pip show bleach`: 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 bleach.
- 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-vv2x-vrpj-qqpq (OSV record GHSA-vv2x-vrpj-qqpq lists affected ranges: PyPI bleach >=0 <3.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-vv2x-vrpj-qqpq (GitHub-reviewed advisory GHSA-vv2x-vrpj-qqpq lists affected ranges: PyPI bleach >=0 <3.3.0)

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