{"id":"GHSA-m6xf-fq7q-8743","summary":"Bleach vulnerable to mutation XSS via whitelisted math or svg and raw tag","details":"### Impact\n\nA [mutation XSS](https://cure53.de/fp170.pdf) affects users calling `bleach.clean` with all of:\n\n* the `svg` or `math` in the allowed/whitelisted tags\n* an RCDATA tag (see below) in the allowed/whitelisted tags\n* the keyword argument `strip=False`\n\n### Patches\n\nUsers are encouraged to upgrade to bleach v3.1.2 or greater.\n\n### Workarounds\n\n* modify `bleach.clean` calls to use `strip=True`, or not whitelist `math` or `svg` tags and one or more of the following tags:\n\n```\nscript\nnoscript\nstyle\nnoframes\nxmp\nnoembed\niframe\n```\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=1621692\n* https://cure53.de/fp170.pdf\n* https://nvd.nist.gov/vuln/detail/CVE-2020-6816\n* https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach\n\n### Credits\n\n* Reported by [Yaniv Nizry](https://twitter.com/ynizry) from the CxSCA AppSec group at Checkmarx\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-2020-6816","PYSEC-2020-28"],"modified":"2026-05-07T05:00:25.771889194Z","published":"2020-03-24T15:06:32Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2020-03-23T22:25:38Z","nvd_published_at":"2020-03-24T22:15:00Z","cwe_ids":["CWE-79"],"severity":"MODERATE"},"references":[{"type":"WEB","url":"https://github.com/mozilla/bleach/security/advisories/GHSA-m6xf-fq7q-8743"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-6816"},{"type":"WEB","url":"https://advisory.checkmarx.net/advisory/CX-2020-4277"},{"type":"PACKAGE","url":"https://github.com/mozilla/bleach"},{"type":"WEB","url":"https://github.com/mozilla/bleach/releases/tag/v3.1.2"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2020-28.yaml"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/EDQU2SZLZMSSACCBUBJ6NOSRNNBDYFW5"},{"type":"WEB","url":"https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach"}],"affected":[{"package":{"name":"bleach","ecosystem":"PyPI","purl":"pkg:pypi/bleach"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.2"}]}],"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"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2020/03/GHSA-m6xf-fq7q-8743/GHSA-m6xf-fq7q-8743.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:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"}]}