CVE-2026-102277: brace-expansion Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q2hr-2g5m-vwhr",
  "modified" : "2026-09-29T23:45:39Z",
  "published" : "2026-09-29T23:45:39Z",
  "aliases" : [ "CVE-2026-102277" ],
  "summary" : "brace-expansion: Quadratic-time expansion of the `{a},b}` rewrite causes CPU denial of service",
  "details" : "### Summary\n\nExpanding `{a},b}`-shaped input takes time quadratic in the number of literal `}` characters, blocking the event loop.\n\nBash preserves a quirk where a brace group followed by a comma set still expands (`{a},b}`). The parser implements this by rewriting the string and restarting the scan. Each pass absorbs exactly one `}` and re-scans from the beginning, so `n` trailing braces cost `n` full passes.\n\n### Reproduction\n\n```js\nconst build = n => '{a}' + '}'.repeat(n) + ',z}'\n\nfor (const n of [8000, 16000, 32000, 64000, 128000]) {\n  const t = Date.now()\n  expand(build(n))\n  console.log(n, Date.now() - t + 'ms')\n}\n```\n\n| n | input | time | results |\n|---|---|---|---|\n| 8,000 | 8 KB | 110 ms | 2 |\n| 16,000 | 16 KB | 446 ms | 2 |\n| 32,000 | 32 KB | 1.7 s | 2 |\n| 64,000 | 64 KB | 6.9 s | 2 |\n| 128,000 | 128 KB | **27.7 s** | 2 |\n\n`ms/n^2` is flat at ~1.7 and each doubling of `n` costs exactly 4.0x - quadratic. 128 KB of input blocks the event loop for nearly half a minute to produce two results.\n\n### Mechanism\n\nInstrumenting the rewrite branch confirms it runs exactly `n + 1` times, once per literal `}`, each re-scanning the whole string.\n\nThere is a second multiplier. The rewrite replaces the group's closing `}` with the internal `escClose` sentinel, which is `'\\0CLOSE' + Math.random() + '\\0'` - about 25 characters. The working string therefore *grows* by ~25 characters on every pass:\n\n| n | input length | final string length |\n|---|---|---|\n| 1,000 | 1,006 | 26,006 |\n| 8,000 | 8,006 | 208,006 |\n\nSo the input is inflated roughly 26x, and that factor multiplies both the quadratic constant and peak memory. This makes it partly a memory-pressure issue as well as a CPU one.\n\n### Why `max` and `maxLength` do not help\n\nThe cost is in parsing, before the result set exists. The payload yields 2 results regardless of size, so neither bound is ever reached.\n\n### Impact\n\nAn application passing an untrusted pattern to `expand()`, directly or through `minimatch` / `glob`, can have its event loop blocked for tens of seconds by a payload well under minimatch's 65,536-character cap. For a single-threaded Node server that is a full stall, not just a slow request.\n\nDegraded availability rather than a crash - the process recovers once the expansion completes.\n\n### Affected versions\n\nVerified affected on 1.1.18, 2.1.4, 3.0.6 and 5.0.9, all within a few percent of each other (~460-490 ms at n=16,000).\n\n### Patch\n\nThe rewrite loop gets an iteration bound. Past the cap the remaining string is treated as non-expanding and returned literally, consistent with the existing `max` / `maxLength` caps, which truncate rather than throw.\n\nNote this bounds the number of passes, not the cost of each: worst-case work remains proportional to `cap x input length`. The cap is set low enough that the residual is bounded in practice, and far above what any realistic `{a},b}` input needs.\n\n### Severity note\n\nScored 5.3 Medium (`A:L`) for consistency with GHSA-3jxr-9vmj-r5cp, the other algorithmic-complexity advisory on this package (CWE-407), which uses the same vector. The stack-exhaustion advisories on this package score `A:H` because they crash the process outright; this one stalls it.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "5.0.12"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.0.9"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.1.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "brace-expansion"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.1.21"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/security/advisories/GHSA-q2hr-2g5m-vwhr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-102277"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/33a5ef17b8d800bbfa8c52b14c39043b6aac1a96"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/bdff773f98e5988616b7039cc9b508df5d640b22"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/c55e67d8d8b1c56a2474afff15c2891166b2d364"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/juliangruber/brace-expansion/commit/ffdfa3e3806bed17c0874b8f1439b084de354a7e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/juliangruber/brace-expansion"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-407" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T23:45:39Z",
    "nvd_published_at" : "2026-09-28T21:17:16Z"
  }
}