GHSA-Q2HR-2G5M-VWHR
Vulnerability from github – Published: 2026-09-29 23:45 – Updated: 2026-09-29 23:45Summary
Expanding {a},b}-shaped input takes time quadratic in the number of literal } characters, blocking the event loop.
Bash 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.
Reproduction
const build = n => '{a}' + '}'.repeat(n) + ',z}'
for (const n of [8000, 16000, 32000, 64000, 128000]) {
const t = Date.now()
expand(build(n))
console.log(n, Date.now() - t + 'ms')
}
| n | input | time | results |
|---|---|---|---|
| 8,000 | 8 KB | 110 ms | 2 |
| 16,000 | 16 KB | 446 ms | 2 |
| 32,000 | 32 KB | 1.7 s | 2 |
| 64,000 | 64 KB | 6.9 s | 2 |
| 128,000 | 128 KB | 27.7 s | 2 |
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.
Mechanism
Instrumenting the rewrite branch confirms it runs exactly n + 1 times, once per literal }, each re-scanning the whole string.
There 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 | input length | final string length |
|---|---|---|
| 1,000 | 1,006 | 26,006 |
| 8,000 | 8,006 | 208,006 |
So 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.
Why max and maxLength do not help
The cost is in parsing, before the result set exists. The payload yields 2 results regardless of size, so neither bound is ever reached.
Impact
An 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.
Degraded availability rather than a crash - the process recovers once the expansion completes.
Affected versions
Verified 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).
Patch
The 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.
Note 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.
Severity note
Scored 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.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "4.0.0"
},
{
"fixed": "5.0.12"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "3.0.9"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "2.0.0"
},
{
"fixed": "2.1.7"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.1.21"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-102277"
],
"database_specific": {
"cwe_ids": [
"CWE-400",
"CWE-407"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-29T23:45:39Z",
"nvd_published_at": "2026-09-28T21:17:16Z",
"severity": "MODERATE"
},
"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 =\u003e \u0027{a}\u0027 + \u0027}\u0027.repeat(n) + \u0027,z}\u0027\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 + \u0027ms\u0027)\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\u0027s closing `}` with the internal `escClose` sentinel, which is `\u0027\\0CLOSE\u0027 + Math.random() + \u0027\\0\u0027` - 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\u0027s 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.",
"id": "GHSA-q2hr-2g5m-vwhr",
"modified": "2026-09-29T23:45:39Z",
"published": "2026-09-29T23:45:39Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
],
"summary": "brace-expansion: Quadratic-time expansion of the `{a},b}` rewrite causes CPU denial of service"
}
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