CVE-2025-68142: Pymdown extensions Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-r6h4-mm7h-8pmq",
  "modified" : "2025-12-16T20:46:05Z",
  "published" : "2025-12-16T20:46:05Z",
  "aliases" : [ "CVE-2025-68142" ],
  "summary" : "PyMdown Extensions has a ReDOS bug in its Figure Capture extension",
  "details" : "### Impact\n\nThis issue describes a ReDOS bug found within the figure caption extension (`pymdownx.blocks.caption` ).\n\nIn systems that take unchecked user content, this could cause long hangs when processing the data if a malicious payload was crafted.\n\n### Patches\n\nThis issue is patched in Release [10.16.1](https://pypi.org/project/pymdown-extensions/10.16.1/).\n\n### Workarounds\n\nSome possible workarounds\n\nIf users are concerned about this vulnerability and process unknown user content without timeouts or other safeguards in place to prevent really large, malicious content being aimed at systems, the use of `pymdownx.blocks.caption` could be avoided until the library is updated to 10.16.1+.\n\n### References\n\nThe original issue https://github.com/facelessuser/pymdown-extensions/issues/2716.\n\n### Description\n\nThe original issue came through PyMdown Extensions' normal issue tracker instead of the typical security flow: https://github.com/facelessuser/pymdown-extensions/issues/2716. Because this came through the normal issue flow, it was handled as a normal issue. In the future, PyMdown Extensions will ensure such issues, even if prematurely made public through the normal issue flow, are redirected through the typical security process.\n\nThe regular expression pattern in question is as follows:\n\n```py\nRE_FIG_NUM = re.compile(r'^(\\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)')\n```\n\nThe POC was provided by @ShangzhiXu\n\n```py\nimport re\nimport time\n\nregex_pattern = re.compile(r'^(\\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)')\n\nfor i in range(50, 500, 50):\n    long_string = '1' * i + 'a'\n    start_time = time.time()\n    match = re.match(regex_pattern, long_string)\n    end_time = time.time()\n    print(f\"long_string execution time: {end_time - start_time:.6f} s\")\n```\n\nThe issue with the above pattern is that `.` was used, which accepts any character when we meant to use `\\.`. The fix was to update the pattern to:\n\n```py\nRE_FIG_NUM = re.compile(r'^(\\^)?([1-9][0-9]*(?:\\.[1-9][0-9]*)*)(?= |$)')\n```\n\nRelevant PR with fix: https://github.com/facelessuser/pymdown-extensions/pull/2717\n\n### Version(s) & System Info\n\n- Operating System: Any\n- Python Version: Any",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pymdown-extensions"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "10.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-r6h4-mm7h-8pmq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-68142"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/facelessuser/pymdown-extensions/commit/b50d15a56850ed1408a284bba81cc019c6bd72e8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/facelessuser/pymdown-extensions"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/pymdown-extensions/10.16.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-16T20:46:05Z",
    "nvd_published_at" : "2025-12-16T18:16:16Z"
  }
}