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BREW-UM-CVE-2021-28834 (GHSA-52P9-V744-MWJJ)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:46 – Updated: 2026-08-13 17:46 – Source website
VLAI
Summary
Remote code execution in Kramdown
Details

Kramdown before 2.3.1 does not restrict Rouge formatters to the Rouge::Formatters namespace, and thus arbitrary classes can be instantiated.

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "kramdown",
        "resource_purl": "pkg:gem/kramdown@1.17.0",
        "upstream_fixed_in": "2.3.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "um",
        "purl": "pkg:brew/um"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "RubyGems",
        "key": "pkg:gem/kramdown@1.17.0",
        "name": "kramdown",
        "resource": "kramdown",
        "strategy": "registry",
        "subject_version": "1.17.0"
      }
    ]
  },
  "details": "Kramdown before 2.3.1 does not restrict Rouge formatters to the Rouge::Formatters namespace, and thus arbitrary classes can be instantiated.",
  "id": "BREW-um-CVE-2021-28834",
  "modified": "2026-08-13T17:46:08Z",
  "published": "2026-08-13T17:46:08Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-28834"
    },
    {
      "type": "WEB",
      "url": "https://github.com/gettalong/kramdown/pull/708"
    },
    {
      "type": "WEB",
      "url": "https://github.com/stanhu/kramdown/commit/d6a1cbcb2caa2f8a70927f176070d126b2422760"
    },
    {
      "type": "WEB",
      "url": "https://github.com/stanhu/kramdown/commit/ff0218aefcf00cd5a389e17e075d36cd46d011e2"
    },
    {
      "type": "WEB",
      "url": "https://about.gitlab.com/releases/2021/03/17/security-release-gitlab-13-9-4-released/#remote-code-execution-via-unsafe-user-controlled-markdown-rendering-options"
    },
    {
      "type": "WEB",
      "url": "https://github.com/gettalong/kramdown/compare/REL_2_3_0...REL_2_3_1"
    },
    {
      "type": "WEB",
      "url": "https://gitlab.com/gitlab-org/gitlab/-/commit/179329b5c3c118924fb242dc449d06b4ed6ccb66"
    },
    {
      "type": "WEB",
      "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NJCJVYHPY6LNUFM6LYZIAUIYOMVT5QGV"
    },
    {
      "type": "WEB",
      "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/S3BBLUIDCUUR3NEE4NJLOCCAV3ALQ3O6"
    },
    {
      "type": "WEB",
      "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/SYOLQKFL6IJCQLBXV34Z4TI4O54GESPR"
    },
    {
      "type": "WEB",
      "url": "https://www.debian.org/security/2021/dsa-4890"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Remote code execution in Kramdown",
  "upstream": [
    "GHSA-52p9-v744-mwjj",
    "CVE-2021-28834"
  ]
}



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