CVE-2021-21236: CairoSVG Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hq37-853p-g5cf",
  "modified" : "2024-09-13T17:42:15Z",
  "published" : "2021-01-06T16:57:50Z",
  "aliases" : [ "CVE-2021-21236" ],
  "summary" : "Regular Expression Denial of Service in CairoSVG",
  "details" : "# Doyensec Vulnerability Advisory \n\n* Regular Expression Denial of Service (REDoS) in cairosvg\n* Affected Product: CairoSVG v2.0.0+\n* Vendor: https://github.com/Kozea\n* Severity: Medium\n* Vulnerability Class: Denial of Service\n* Author(s): Ben Caller ([Doyensec](https://doyensec.com))\n\n## Summary\n\nWhen processing SVG files, the python package CairoSVG uses two regular expressions which are vulnerable to Regular Expression Denial of Service (REDoS).\nIf an attacker provides a malicious SVG, it can make cairosvg get stuck processing the file for a very long time.\n\n## Technical description\n\nThe vulnerable regular expressions are\n\nhttps://github.com/Kozea/CairoSVG/blob/9c4a982b9a021280ad90e89707eacc1d114e4ac4/cairosvg/colors.py#L190-L191\n\nThe section between 'rgb(' and the final ')' contains multiple overlapping groups.\n\nSince all three infinitely repeating groups accept spaces, a long string of spaces causes catastrophic backtracking when it is not followed by a closing parenthesis.\n\nThe complexity is cubic, so doubling the length of the malicious string of spaces makes processing take 8 times as long.\n\n## Reproduction steps\n\nCreate a malicious SVG of the form:\n\n    <svg width=\"1\" height=\"1\"><rect fill=\"rgb(                     ;\"/></svg>\n\nwith the following code:\n\n    '<svg width=\"1\" height=\"1\"><rect fill=\"rgb(' + (' ' * 3456) + ';\"/></svg>'\n\nNote that there is no closing parenthesis before the semi-colon.\n\nRun cairosvg e.g.:\n\n    cairosvg cairo-redos.svg -o x.png\n\nand notice that it hangs at 100% CPU. Increasing the number of spaces increases the processing time with cubic complexity.\n\n## Remediation\n\nFix the regexes to avoid overlapping parts. Perhaps remove the [ \\n\\r\\t]* groups from the regex, and use .strip() on the returned capture group.\n\n## Disclosure timeline\n\n- 2020-12-30: Vulnerability disclosed via email to CourtBouillon",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "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/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "CairoSVG"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.5.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Kozea/CairoSVG/security/advisories/GHSA-hq37-853p-g5cf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21236"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Kozea/CairoSVG/commit/cfc9175e590531d90384aa88845052de53d94bf3"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Kozea/CairoSVG"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Kozea/CairoSVG/releases/tag/2.5.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/cairosvg/PYSEC-2021-5.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/CairoSVG"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-01-06T16:57:38Z",
    "nvd_published_at" : "2021-01-06T17:15:00Z"
  }
}