{"id":"CVE-2026-14257","aliases":["GHSA-mh99-v99m-4gvg"],"url":"https://o3.security/vulnerability/CVE-2026-14257","summary":"brace-expansion DoS via unbounded expansion length causing an out-of-memory process crash","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 — plus the intermediate\narrays combined at each brace group — 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 (`'{a,b}'.repeat(1500)`) is enough to crash a default Node\nprocess.\n\n### Details\n\nFor `N` chained brace groups such as `'{a,b}'.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 × 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) : ['']\n...\nfor (let j = 0; j < N.length; j++) {\n  for (let k = 0; k < post.length && expansions.length < 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 < 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 —\nbecause V8 represents `pre + N[j] + post[k]` as a cons-string (rope) that\nreferences `post[k]` — those intermediate strings stay reachable through the\nwhole chain. Memory therefore scales with `max × N`.\n\nMeasured on `5.0.7` (`'{a,b}'.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 | — | **OOM crash** |\n\n### Proof of concept\n\n```js\nconst { expand } = require('brace-expansion')\n\n// ~7.5 KB input — crashes the process with a fatal, uncatchable OOM:\n//   FATAL ERROR: ... JavaScript heap out of memory\ntry {\n  expand('{a,b}'.repeat(1500))\n} catch (e) {\n  // never reached — the process is already dead\n}\n```\n\n### Impact\n\nAny application that passes attacker-influenced strings to\n`brace-expansion.expand()` — directly, or transitively via `minimatch` / `glob`\nbrace patterns — 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 — consistent with how `max` already truncates —\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, `'{a,b}'.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 × 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't possible, avoid passing untrusted input to\n`expand()` / glob brace patterns, or pass a small explicit `max` **and**\n`maxLength`.","published":"2026-07-23T12:54:23.124Z","modified":"2026-10-21T02:30:57.254085931Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00643,"percentile":0.49199,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"brace-expansion","fixedVersion":"5.0.8"},{"ecosystem":"npm","name":"brace-expansion","fixedVersion":"3.0.3"},{"ecosystem":"npm","name":"brace-expansion","fixedVersion":"2.1.3"},{"ecosystem":"npm","name":"brace-expansion","fixedVersion":"1.1.17"}],"fix":{"url":"https://github.com/juliangruber/brace-expansion/commit/a1bd33999ea75262c4749fff3bbb0d1372bd07b5","label":"juliangruber/brace-expansion@a1bd339"},"references":[{"type":"WEB","url":"https://www.npmjs.com/package/brace-expansion"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/14xxx/CVE-2026-14257.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-14257"},{"type":"FIX","url":"https://github.com/juliangruber/brace-expansion/commit/a1bd33999ea75262c4749fff3bbb0d1372bd07b5"},{"type":"PACKAGE","url":"https://github.com/juliangruber/brace-expansion"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/security/advisories/GHSA-mh99-v99m-4gvg"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/pull/129"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/pull/130"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/pull/136"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/commit/139d015104e71433ad52a41d19467c48ecbb2c7d"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/commit/cb4b9e47cc2ec777c14b2b4492fb431a56f6a031"},{"type":"WEB","url":"https://github.com/juliangruber/brace-expansion/commit/d13ff455a58b0d56704f0111e3c2a0b16ceb06eb"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:30:57.254085931Z"}}