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BREW-RESTVIEW-CVE-2020-6817 (GHSA-VQHP-CXGC-6WMM)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:32 – Updated: 2026-09-10 01:05 – Source website
VLAI
Summary
regular expression denial-of-service (ReDoS) in Bleach
Details

Impact

bleach.clean behavior parsing style attributes could result in a regular expression denial of service (ReDoS).

Calls to bleach.clean with an allowed tag with an allowed style attribute are vulnerable to ReDoS. For example, bleach.clean(..., attributes={'a': ['style']}).

Patches

3.1.4

Workarounds

  • do not whitelist the style attribute in bleach.clean calls

  • limit input string length

References

  • https://bugzilla.mozilla.org/show_bug.cgi?id=1623633
  • https://www.regular-expressions.info/redos.html
  • https://blog.r2c.dev/posts/finding-python-redos-bugs-at-scale-using-dlint-and-r2c/
  • https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-6817

Credits

  • Reported by schwag09 of r2c

For more information

If you have any questions or comments about this advisory:

  • Open an issue at https://github.com/mozilla/bleach/issues
  • Email us at security@mozilla.org
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/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": "3.1.4"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "restview",
        "purl": "pkg:brew/restview"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.0.2_2"
            }
          ],
          "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\n`bleach.clean` behavior parsing style attributes could result in a regular expression denial of service (ReDoS).\n\nCalls to ``bleach.clean`` with an allowed tag with an allowed ``style`` attribute are vulnerable to ReDoS. For example, ``bleach.clean(..., attributes={\u0027a\u0027: [\u0027style\u0027]})``.\n\n### Patches\n\n3.1.4\n\n### Workarounds\n\n* do not whitelist the style attribute in `bleach.clean` calls\n\n* limit input string length\n\n### References\n\n* https://bugzilla.mozilla.org/show_bug.cgi?id=1623633\n* https://www.regular-expressions.info/redos.html\n* https://blog.r2c.dev/posts/finding-python-redos-bugs-at-scale-using-dlint-and-r2c/\n* https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-6817\n\n### Credits\n\n* Reported by schwag09 of r2c\n\n### For more information\nIf you have any questions or comments about this advisory:\n\n* Open an issue at https://github.com/mozilla/bleach/issues\n* Email us at security@mozilla.org",
  "id": "BREW-restview-CVE-2020-6817",
  "modified": "2026-09-10T01:05:59Z",
  "published": "2026-08-13T17:32:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mozilla/bleach/security/advisories/GHSA-vqhp-cxgc-6wmm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2020-6817"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1623633"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mozilla/bleach"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mozilla/bleach/releases/tag/v3.1.4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2020-340.yaml"
    },
    {
      "type": "WEB",
      "url": "https://snyk.io/vuln/SNYK-PYTHON-BLEACH-561754"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "regular expression denial-of-service (ReDoS) in Bleach",
  "upstream": [
    "GHSA-vqhp-cxgc-6wmm",
    "CVE-2020-6817",
    "PYSEC-2020-340",
    "SNYK-PYTHON-BLEACH-561754"
  ]
}



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