{"id":"GHSA-vv2x-vrpj-qqpq","summary":"Cross-site scripting in Bleach","details":"### Impact                                                                                                                                                                                                                                                    \n\nA [mutation XSS](https://cure53.de/fp170.pdf) affects users calling `bleach.clean` with all of:\n\n* `svg` or `math` in the allowed tags\n* `p` or `br` in allowed tags\n* `style`, `title`, `noscript`, `script`, `textarea`, `noframes`, `iframe`, or `xmp` in allowed tags\n* the keyword argument `strip_comments=False`\n\nNote: none of the above tags are in the default allowed tags and `strip_comments` defaults to `True`.\n\n### Patches\n\nUsers are encouraged to upgrade to bleach v3.3.0 or greater.\n\nNote: bleach v3.3.0 introduces a breaking change to escape HTML comments by default.\n\n### Workarounds\n\n* modify `bleach.clean` calls to at least one of:\n  * not allow the `style`, `title`, `noscript`, `script`, `textarea`, `noframes`, `iframe`, or `xmp` tag\n  * not allow `svg` or `math` tags\n  * not allow `p` or `br` tags\n  * set `strip_comments=True`\n\n* A strong [Content-Security-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) without `unsafe-inline` and `unsafe-eval` [`script-src`s](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src)) will also help mitigate the risk.\n\n### References\n\n* https://bugzilla.mozilla.org/show_bug.cgi?id=1689399\n* https://advisory.checkmarx.net/advisory/CX-2021-4303\n* https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-23980\n* https://cure53.de/fp170.pdf\n\n### Credits\n\n* Reported by [Yaniv Nizry](https://twitter.com/ynizry) from the CxSCA AppSec group at Checkmarx\n* Additional eject tags not mentioned in the original advisory and the CSP mitigation line being truncated in the revised advisory reported by [Michał Bentkowski](https://twitter.com/SecurityMB) at Securitum\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n* Open an issue at [https://github.com/mozilla/bleach/issues](https://github.com/mozilla/bleach/issues)\n* Email us at [security@mozilla.org](mailto:security@mozilla.org)","aliases":["CVE-2021-23980","PYSEC-2021-865"],"modified":"2026-05-07T05:02:29.291934374Z","published":"2021-02-02T17:58:40Z","database_specific":{"cwe_ids":["CWE-79"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2021-02-02T15:54:20Z","nvd_published_at":"2023-02-16T22:15:00Z"},"references":[{"type":"WEB","url":"https://github.com/mozilla/bleach/security/advisories/GHSA-vv2x-vrpj-qqpq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-23980"},{"type":"WEB","url":"https://github.com/mozilla/bleach/commit/79b7a3c5e56a09d1d323a5006afa59b56162eb13"},{"type":"WEB","url":"https://advisory.checkmarx.net/advisory/CX-2021-4303"},{"type":"WEB","url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1689399"},{"type":"WEB","url":"https://bugzilla.mozilla.org/show_bug.cgi?id=CVE-2021-23980"},{"type":"WEB","url":"https://cure53.de/fp170.pdf"},{"type":"PACKAGE","url":"https://github.com/mozilla/bleach"},{"type":"WEB","url":"https://github.com/mozilla/bleach/blob/79b7a3c5e56a09d1d323a5006afa59b56162eb13/CHANGES#L4"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2021-865.yaml"},{"type":"WEB","url":"https://pypi.org/project/bleach"}],"affected":[{"package":{"name":"bleach","ecosystem":"PyPI","purl":"pkg:pypi/bleach"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.3.0"}]}],"versions":["0.1","0.1.1","0.1.2","0.2","0.2.1","0.2.2","0.3","0.3.1","0.3.3","0.3.4","0.5.0","0.5.1","1.0.0","1.0.1","1.0.2","1.0.3","1.0.4","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.1.5","1.2","1.2.1","1.2.2","1.4","1.4.1","1.4.2","1.4.3","1.5.0","2.0.0","2.1","2.1.1","2.1.2","2.1.3","2.1.4","3.0.0","3.0.1","3.0.2","3.1.0","3.1.1","3.1.2","3.1.3","3.1.4","3.1.5","3.2.0","3.2.1","3.2.2","3.2.3"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/02/GHSA-vv2x-vrpj-qqpq/GHSA-vv2x-vrpj-qqpq.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},{"type":"CVSS_V4","score":"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"}]}