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node_modules/brace-expansion/ADVISORY-CVE-2026-14257.md

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+# DoS via unbounded expansion length — out-of-memory process crash
+
+- **CVE:** CVE-2026-14257
+- **Package:** brace-expansion (npm)
+- **Reporter:** @bnbdr
+- **Severity (proposed):** High — `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` (7.5)
+- **Weakness:** CWE-770 (Allocation of Resources Without Limits or Throttling) / CWE-400 (Uncontrolled Resource Consumption)
+- **Affected:** all versions up to and including `5.0.7` (the `1.x`, `2.x`, `3.x` and `4.x` lines share the same combine logic and are expected to be affected)
+
+### 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:
+
+```js
+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
+
+```js
+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`.