{
"id": "GHSA-vv2x-vrpj-qqpq",
"aliases": [
"CVE-2021-23980"
],
"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 [[email protected] ](mailto:[email protected] )",
"summary": "Cross-site scripting in Bleach",
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "3.3.0"
}
]
}
],
"package": {
"name": "bleach",
"ecosystem": "PyPI"
}
}
],
"modified": "2025-03-20T18:50:31Z",
"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"
}
],
"published": "2021-02-02T17:58:40Z",
"references": [
{
"url": "https://github.com/mozilla/bleach/security/advisories/GHSA-vv2x-vrpj-qqpq",
"type": "WEB"
},
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-23980",
"type": "ADVISORY"
},
{
"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": "WEB"
},
{
"url": "https://github.com/mozilla/bleach",
"type": "PACKAGE"
},
{
"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",
"type": "WEB"
}
],
"schema_version": "1.4.0",
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"severity": "MODERATE",
"github_reviewed": true,
"nvd_published_at": "2023-02-16T22:15:00Z",
"github_reviewed_at": "2021-02-02T15:54:20Z"
}
}