Vulnerability details

### Summary `expand_()` recurses once per level of brace *nesting*. Deeply nested input exhausts the native stack and crashes the process. This is distinct from CVE-2026-14257 / GHSA-mh99-v99m-4gvg, which made the *tail* iterative (recursion on `m.post`, driven by how many groups are chained). Nesting depth drives a different recursion that the tail fix never touched, so the documented constant-stack-depth guarantee only ever covered chained input, not nested input. It is also distinct from GHSA-6j4f-fj2g-mc7p, which fixed recursion in `parseCommaParts()`. Both payloads below still crash with that fix applied. ### Two recursion sites **Comma members.** Each alternative of a brace set is expanded by a recursive call, so nesting a set inside every alternative recurses once per level: ```js expand('{a,'.repeat(4000) + 'z' + '}'.repeat(4000)) // RangeError: Maximum call stack size exceeded ``` Crashes at depth 3,907 - about **15.6 KB** of input. **Single set.** A brace set whose body parses to a single part is expanded by a recursive call before being re-wrapped (`x{{a,b}}y` -> `x{a}y x{b}y`), which recurses once per nesting level: ```js expand('{'.repeat(3200) + 'a,b' + '}'.repeat(3200)) // RangeError: Maximum call stack size exceeded ``` Crashes at depth 3,125 - about **6.25 KB** of input. This is the cheapest stack-exhaustion payload known against this package: roughly a quarter the input of GHSA-6j4f-fj2g-mc7p (29 KB), and about a tenth of minimatch's `MAX_PATTERN_LENGTH` (65,536). ### Why `max` and `maxLength` do not help Both crashes happen while recursing into sub-expansions, before the result set grows. The payloads produce almost no output - the single-set case yields 2 results - so neither bound is ever the limiter. `expand(payload, { max: 1, maxLength: 1 })` still overflows. ### Impact Any application passing an untrusted string to `expand()`, directly or through `minimatch` / `glob` as a user-supplied glob pattern, can be crashed. In Node a `RangeError` the application does not catch terminates the process, so a server globbing user input is exposed to remote unauthenticated denial of service. Availability only. No code execution, no data exposure. ### Affected versions Verified affected on 1.1.18, 2.1.4, 3.0.6 and 5.0.9, at near-identical depths on every line (single set: 3,125 on all four; comma members: 3,907-4,102). Not a regression from any recent fix - the gap predates them. ### Patch A `maxDepth` bound (default `EXPANSION_MAX_DEPTH`) is threaded through `expand_()`. Past the cap a group is treated as non-expanding and returned literally, which is how the parser already handles a group that cannot expand. This matches the existing `max` / `maxLength` caps, which truncate rather than throw, so `expand()` continues never to throw on any input. The default sits far above any realistic nesting depth and well below the crash threshold.