CVE-2026-13149: brace-expansion Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3jxr-9vmj-r5cp",
  "modified" : "2026-07-20T20:51:10Z",
  "published" : "2026-07-20T20:51:09Z",
  "aliases" : [ "CVE-2026-13149" ],
  "summary" : "brace-expansion: DoS via exponential-time expansion of consecutive non-expanding {} groups",
  "details" : "### Summary\nbrace-expansion's expand() exhibits exponential-time - O(2ⁿ) - behavior in the number of consecutive non-expanding {} groups. A short, all-ASCII input (~90 bytes/30 groups) blocks the calling thread for minutes; a slightly longer input hangs it effectively indefinitely. Because the dominant consumers run on Node's single-threaded event loop, one small input can fully stall a worker/process.\n\nIn `expand_`, `post` is computed unconditionally at the top of the function, before the early-return branches that don't use it:\n```js\nconst post = m.post.length ? expand_(m.post, max, false) : [''];   // always recurses\n  ...\nif (!isSequence && !isOptions) {\n  if (m.post.match(/,(?!,).*\\}/)) {\n    str = m.pre + '{' + m.body + escClose + m.post;\n    return expand_(str, max, true); // restart — `post` discarded\n  }\n  return [str];\n}\n```\n\nFor input like a{},{},…, the first {} is non-expanding, so control reaches the {a},b} rewrite branch - but `expand_` has already recursed into post over the entire remaining tail, only to throw the result away.\nEach level therefore spawns two recursive expansions over essentially the same remaining work: `T(n) = 2·T(n−1) ⇒ O(2ⁿ)`.\n\nThe max option does not mitigate this: max only bounds the output-building loops; neither the post recursion nor the rewrite recursion consults it.\n  \nMeasured on 5.0.6:\n\n| groups (n) | input bytes | time |\n|---|---|---|\n| 20 | 60 | 130 ms |\n| 24 | 72 | 1.9 s |\n| 26 | 78 | 7.8 s |\n| 30 (PoC) | 90 | ~2 min |\n\n### Proof of concept\n```js\nconst { expand } = require('brace-expansion');\n// 30 non-expanding groups, ~90 bytes — blocks for minutes:\nexpand('a{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{}');\n```\n\n### Impact\n\nAny application that passes attacker-influenced strings to brace-expansion.expand() - directly or transitively via minimatch/glob brace patterns - can be driven into a multi-minute-to-indefinite CPU hang by a tiny request, denying service on that thread/process.\n\n### Remediation\n\nUpgrade to a patched release. The fix:\n1. Defers computing post until after the early-return branches (and computes it locally in the $-suffix branch), so post is only expanded when a brace set actually expands and the value is used. This alone removes the exponential.\n1. Converts the {a},b} rewrite from recursion to an in-function loop, so a long run of rewrites cannot grow the call stack.\n\nVerified: the PoC drops from ~2 min to 0.55 ms, 5,000 groups complete in ~344 ms, and output is identical to 5.0.6 across a behavioral-equivalence suite (sequences, padding, $-prefix, a{},b}c, {},a}b, x{{a,b}}y, etc.). Post-fix complexity is ~O(n²) on this input class - acceptable for the security fix; a linear rewrite can be a non-urgent follow-up.\n\nIf immediate upgrade isn't possible, avoid passing untrusted input to expand() / glob brace patterns, or run such expansion under a timeout/worker.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  }, {
    "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/S:N/AU:Y/R:U/V:D/RE:M/U:Amber"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "5.0.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.1.16"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.1.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/security/advisories/GHSA-3jxr-9vmj-r5cp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-13149"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/pull/122"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/pull/123"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/835d6be91201122d9adffb0c0c8c094189ace265"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/c7e33ec13ac1a684c116720843ce24e208611754"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/d74e63030c012e3b7ae81657b8d665619cd51b95"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/juliangruber/brace-expansion"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/releases/tag/v1.1.16"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/releases/tag/v2.1.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/releases/tag/v5.0.7"
  }, {
    "type" : "WEB",
    "url" : "https://www.npmjs.com/package/brace-expansion"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-20T20:51:09Z",
    "nvd_published_at" : "2026-06-30T10:16:34Z"
  }
}