Vulnerability-Lookup

GHSA-MH99-V99M-4GVG

Vulnerability from github – Published: 2026-07-24 21:53 – Updated: 2026-07-24 21:53

Summary

brace-expansion: DoS via unbounded expansion length causing an out-of-memory process crash

Details

Summary

expand() bounds the number of results it produces (the max option, 100_000 by default) but not their length. By chaining many brace groups, an attacker keeps the result count under max while making every result grow with the number of groups. Building max long results — plus the intermediate arrays combined at each brace group — exhausts memory and crashes the Node process with an uncatchable out-of-memory error. try/catch around expand() does not help: the fatal error terminates the process.

A ~7.5 KB input ('{a,b}'.repeat(1500)) is enough to crash a default Node process.

Details

For N chained brace groups such as '{a,b}'.repeat(N):

the result count is 2^N, immediately capped at max (100_000), so the max protection appears to hold, but
each result is N characters long, so the total output size is max × N characters, which grows without bound in N.

expand_ combines each brace set with the fully-expanded tail:

const post = m.post.length ? expand_(m.post, max, false) : ['']
...
for (let j = 0; j < N.length; j++) {
  for (let k = 0; k < post.length && expansions.length < max; k++) {
    const expansion = pre + N[j] + post[k]   // grows one group longer per level
    ...
    expansions.push(expansion)
  }
}

The loop guard expansions.length < max limits how many strings are built, but nothing limits how long they get. Each recursion level materializes another array of up to max strings, one character longer than the level below, and — because V8 represents pre + N[j] + post[k] as a cons-string (rope) that references post[k] — those intermediate strings stay reachable through the whole chain. Memory therefore scales with max × N.

Measured on 5.0.7 ('{a,b}'.repeat(N), default max):

groups (N)	input bytes	result count	peak RSS
20	100	100,000	~80 MB
50	250	100,000	~214 MB
100	500	100,000	~409 MB
300	1,500	100,000	~1,148 MB
1500	7,500	—	OOM crash

Proof of concept

const { expand } = require('brace-expansion')

// ~7.5 KB input — crashes the process with a fatal, uncatchable OOM:
//   FATAL ERROR: ... JavaScript heap out of memory
try {
  expand('{a,b}'.repeat(1500))
} catch (e) {
  // never reached — the process is already dead
}

Impact

Any application that passes attacker-influenced strings to brace-expansion.expand() — directly, or transitively via minimatch / glob brace patterns — can be crashed by a small request. Because the failure is a fatal V8 out-of-memory error rather than a thrown exception, it cannot be caught and it takes down the whole worker/process, denying service.

Remediation

Upgrade to a patched release. The fix bounds the total number of characters a single expand() call may accumulate (EXPANSION_MAX_LENGTH, default 4_000_000, configurable via a new maxLength option), applied inside the output-building loops so intermediate arrays are bounded too. Once the limit is reached, output is truncated — consistent with how max already truncates — instead of growing without bound. The limit sits well above any realistic expansion (100,000 results hitting max measure ~1M characters), so legitimate input is unaffected.

After the fix, '{a,b}'.repeat(1500) returns a bounded, truncated result in ~0.7 s using ~340 MB and never crashes, including under a constrained 512 MB heap.

The fix bounds memory but the algorithm still rebuilds intermediate arrays at each level (roughly O(N × maxLength) work on this input class). A streaming rewrite that produces output in O(total output size) can be a non-urgent follow-up.

If immediate upgrade isn't possible, avoid passing untrusted input to expand() / glob brace patterns, or pass a small explicit max and maxLength.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.0.7"
      },
      "package": {
        "ecosystem": "npm",
        "name": "brace-expansion"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.0.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-14257"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-24T21:53:14Z",
    "nvd_published_at": "2026-07-23T14:17:00Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`expand()` bounds the *number* of results it produces (the `max` option,\n`100_000` by default) but not their *length*. By chaining many brace groups,\nan attacker keeps the result count under `max` while making every result grow\nwith the number of groups. Building `max` long results \u2014 plus the intermediate\narrays combined at each brace group \u2014 exhausts memory and crashes the Node\nprocess with an **uncatchable** out-of-memory error. `try/catch` around\n`expand()` does not help: the fatal error terminates the process.\n\nA ~7.5 KB input (`\u0027{a,b}\u0027.repeat(1500)`) is enough to crash a default Node\nprocess.\n\n### Details\n\nFor `N` chained brace groups such as `\u0027{a,b}\u0027.repeat(N)`:\n\n- the result count is `2^N`, immediately capped at `max` (`100_000`), so the\n  `max` protection appears to hold, but\n- each result is `N` characters long, so the total output size is\n  `max \u00d7 N` characters, which grows without bound in `N`.\n\n`expand_` combines each brace set with the fully-expanded tail:\n\n```js\nconst post = m.post.length ? expand_(m.post, max, false) : [\u0027\u0027]\n...\nfor (let j = 0; j \u003c N.length; j++) {\n  for (let k = 0; k \u003c post.length \u0026\u0026 expansions.length \u003c max; k++) {\n    const expansion = pre + N[j] + post[k]   // grows one group longer per level\n    ...\n    expansions.push(expansion)\n  }\n}\n```\n\nThe loop guard `expansions.length \u003c max` limits how many strings are built, but\nnothing limits how long they get. Each recursion level materializes another\narray of up to `max` strings, one character longer than the level below, and \u2014\nbecause V8 represents `pre + N[j] + post[k]` as a cons-string (rope) that\nreferences `post[k]` \u2014 those intermediate strings stay reachable through the\nwhole chain. Memory therefore scales with `max \u00d7 N`.\n\nMeasured on `5.0.7` (`\u0027{a,b}\u0027.repeat(N)`, default `max`):\n\n| groups (N) | input bytes | result count | peak RSS |\n|---|---|---|---|\n| 20 | 100 | 100,000 | ~80 MB |\n| 50 | 250 | 100,000 | ~214 MB |\n| 100 | 500 | 100,000 | ~409 MB |\n| 300 | 1,500 | 100,000 | ~1,148 MB |\n| 1500 | 7,500 | \u2014 | **OOM crash** |\n\n### Proof of concept\n\n```js\nconst { expand } = require(\u0027brace-expansion\u0027)\n\n// ~7.5 KB input \u2014 crashes the process with a fatal, uncatchable OOM:\n//   FATAL ERROR: ... JavaScript heap out of memory\ntry {\n  expand(\u0027{a,b}\u0027.repeat(1500))\n} catch (e) {\n  // never reached \u2014 the process is already dead\n}\n```\n\n### Impact\n\nAny application that passes attacker-influenced strings to\n`brace-expansion.expand()` \u2014 directly, or transitively via `minimatch` / `glob`\nbrace patterns \u2014 can be crashed by a small request. Because the failure is a\nfatal V8 out-of-memory error rather than a thrown exception, it cannot be caught\nand it takes down the whole worker/process, denying service.\n\n### Remediation\n\nUpgrade to a patched release. The fix bounds the total number of characters a\nsingle `expand()` call may accumulate (`EXPANSION_MAX_LENGTH`, default\n`4_000_000`, configurable via a new `maxLength` option), applied inside the\noutput-building loops so intermediate arrays are bounded too. Once the limit is\nreached, output is truncated \u2014 consistent with how `max` already truncates \u2014\ninstead of growing without bound. The limit sits well above any realistic\nexpansion (100,000 results hitting `max` measure ~1M characters), so legitimate\ninput is unaffected.\n\nAfter the fix, `\u0027{a,b}\u0027.repeat(1500)` returns a bounded, truncated result in\n~0.7 s using ~340 MB and never crashes, including under a constrained 512 MB\nheap.\n\nThe fix bounds memory but the algorithm still rebuilds intermediate arrays at\neach level (roughly `O(N \u00d7 maxLength)` work on this input class). A streaming\nrewrite that produces output in `O(total output size)` can be a non-urgent\nfollow-up.\n\nIf immediate upgrade isn\u0027t possible, avoid passing untrusted input to\n`expand()` / glob brace patterns, or pass a small explicit `max` **and**\n`maxLength`.",
  "id": "GHSA-mh99-v99m-4gvg",
  "modified": "2026-07-24T21:53:14Z",
  "published": "2026-07-24T21:53:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/juliangruber/brace-expansion/security/advisories/GHSA-mh99-v99m-4gvg"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-14257"
    },
    {
      "type": "WEB",
      "url": "https://github.com/juliangruber/brace-expansion/commit/a1bd33999ea75262c4749fff3bbb0d1372bd07b5"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/juliangruber/brace-expansion"
    },
    {
      "type": "WEB",
      "url": "https://www.npmjs.com/package/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:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "brace-expansion: DoS via unbounded expansion length causing an out-of-memory process crash"
}

CVE-2026-14257 (GCVE-0-2026-14257)

Vulnerability from cvelistv5 – Published: 2026-07-23 12:54 – Updated: 2026-07-23 14:44

Title

brace-expansion DoS via unbounded expansion length causing an out-of-memory process crash

Summary

brace-expansion through 5.0.7 is vulnerable to denial of service via memory exhaustion. The expand() function limits the number of results with a max option (default 100,000) but does not bound the length of each result string. By chaining multiple brace groups, an attacker keeps the result count under the limit while making each result progressively longer, so total memory scales with both count and string length until the process hits a fatal, uncatchable out-of-memory error. About 7.5 KB of input ('{a,b}'.repeat(1500)) crashes a default Node.js process. Any application that passes attacker-influenced strings to brace-expansion.expand() - directly or transitively via minimatch / glob brace patterns - can be crashed by a small request. Fixed in 5.0.8 by adding a maxLength option (default 4,000,000) that bounds accumulated output and intermediate arrays.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-400 - Uncontrolled Resource Consumption
CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

seal

References

3 references

URL	Tags
https://www.npmjs.com/package/brace-expansion
https://github.com/juliangruber/brace-expansion
https://github.com/juliangruber/brace-expansion/c…

Impacted products

1 product

Vendor	Product	Version
juliangruber	brace-expansion	Affected: 0 , ≤ 5.0.7 (semver)

Credits

bnbdr

Show details on NVD website

JSON

To clipboard

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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-MH99-V99M-4GVG

Summary

Details

Proof of concept

Impact

Remediation

CVE-2026-14257 (GCVE-0-2026-14257)

Tags

Sightings

Nomenclature