BREW-JUPYTERLAB-CVE-2020-6816 (GHSA-M6XF-FQ7Q-8743)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:01 – Updated: 2026-09-17 19:02 – Source website
VLAI
Summary
Bleach vulnerable to mutation XSS via whitelisted math or svg and raw tag
Details

Impact

A mutation XSS affects users calling bleach.clean with all of:

  • the svg or math in the allowed/whitelisted tags
  • an RCDATA tag (see below) in the allowed/whitelisted tags
  • the keyword argument strip=False

Patches

Users are encouraged to upgrade to bleach v3.1.2 or greater.

Workarounds

  • modify bleach.clean calls to use strip=True, or not whitelist math or svg tags and one or more of the following tags:
script
noscript
style
noframes
xmp
noembed
iframe

References

  • https://bugzilla.mozilla.org/show_bug.cgi?id=1621692
  • https://cure53.de/fp170.pdf
  • https://nvd.nist.gov/vuln/detail/CVE-2020-6816
  • https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach

Credits

  • Reported by Yaniv Nizry from the CxSCA AppSec group at Checkmarx

For more information

If you have any questions or comments about this advisory:

Severity
6.1 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.3 (Medium)
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
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "bleach",
        "resource_purl": "pkg:pypi/bleach@6.4.0",
        "upstream_fixed_in": "3.1.2"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "jupyterlab",
        "purl": "pkg:brew/jupyterlab"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.2.0"
            },
            {
              "fixed": "2.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/bleach@6.4.0",
        "name": "bleach",
        "resource": "bleach",
        "strategy": "registry",
        "subject_version": "6.4.0"
      }
    ]
  },
  "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)",
  "id": "BREW-jupyterlab-CVE-2020-6816",
  "modified": "2026-09-17T19:02:18Z",
  "published": "2026-08-13T17:01:18Z",
  "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"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Bleach vulnerable to mutation XSS via whitelisted math or svg and raw tag",
  "upstream": [
    "GHSA-m6xf-fq7q-8743",
    "CVE-2020-6816",
    "PYSEC-2020-28"
  ]
}



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