GHSA-3JXR-9VMJ-R5CP
Vulnerability from github – Published: 2026-07-20 20:51 – Updated: 2026-07-20 20:51Summary
brace-expansion's expand() exhibits exponential-time - O(2ⁿ) - behavior in the number of consecutive non-expanding {} groups. A short, all-ASCII input (~90 bytes/30 groups) blocks the calling thread for minutes; a slightly longer input hangs it effectively indefinitely. Because the dominant consumers run on Node's single-threaded event loop, one small input can fully stall a worker/process.
In expand_, post is computed unconditionally at the top of the function, before the early-return branches that don't use it:
const post = m.post.length ? expand_(m.post, max, false) : ['']; // always recurses
...
if (!isSequence && !isOptions) {
if (m.post.match(/,(?!,).*\}/)) {
str = m.pre + '{' + m.body + escClose + m.post;
return expand_(str, max, true); // restart — `post` discarded
}
return [str];
}
For input like a{},{},…, the first {} is non-expanding, so control reaches the {a},b} rewrite branch - but expand_ has already recursed into post over the entire remaining tail, only to throw the result away.
Each level therefore spawns two recursive expansions over essentially the same remaining work: T(n) = 2·T(n−1) ⇒ O(2ⁿ).
The max option does not mitigate this: max only bounds the output-building loops; neither the post recursion nor the rewrite recursion consults it.
Measured on 5.0.6:
| groups (n) | input bytes | time |
|---|---|---|
| 20 | 60 | 130 ms |
| 24 | 72 | 1.9 s |
| 26 | 78 | 7.8 s |
| 30 (PoC) | 90 | ~2 min |
Proof of concept
const { expand } = require('brace-expansion');
// 30 non-expanding groups, ~90 bytes — blocks for minutes:
expand('a{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{}');
Impact
Any application that passes attacker-influenced strings to brace-expansion.expand() - directly or transitively via minimatch/glob brace patterns - can be driven into a multi-minute-to-indefinite CPU hang by a tiny request, denying service on that thread/process.
Remediation
Upgrade to a patched release. The fix: 1. Defers computing post until after the early-return branches (and computes it locally in the $-suffix branch), so post is only expanded when a brace set actually expands and the value is used. This alone removes the exponential. 1. Converts the {a},b} rewrite from recursion to an in-function loop, so a long run of rewrites cannot grow the call stack.
Verified: the PoC drops from ~2 min to 0.55 ms, 5,000 groups complete in ~344 ms, and output is identical to 5.0.6 across a behavioral-equivalence suite (sequences, padding, $-prefix, a{},b}c, {},a}b, x{{a,b}}y, etc.). Post-fix complexity is ~O(n²) on this input class - acceptable for the security fix; a linear rewrite can be a non-urgent follow-up.
If immediate upgrade isn't possible, avoid passing untrusted input to expand() / glob brace patterns, or run such expansion under a timeout/worker.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "5.0.7"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.1.16"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "brace-expansion"
},
"ranges": [
{
"events": [
{
"introduced": "2.0.0"
},
{
"fixed": "2.1.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-13149"
],
"database_specific": {
"cwe_ids": [
"CWE-400",
"CWE-407"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-20T20:51:09Z",
"nvd_published_at": "2026-06-30T10:16:34Z",
"severity": "HIGH"
},
"details": "### Summary\nbrace-expansion\u0027s expand() exhibits exponential-time - O(2\u207f) - behavior in the number of consecutive non-expanding {} groups. A short, all-ASCII input (~90 bytes/30 groups) blocks the calling thread for minutes; a slightly longer input hangs it effectively indefinitely. Because the dominant consumers run on Node\u0027s single-threaded event loop, one small input can fully stall a worker/process.\n\nIn `expand_`, `post` is computed unconditionally at the top of the function, before the early-return branches that don\u0027t use it:\n```js\nconst post = m.post.length ? expand_(m.post, max, false) : [\u0027\u0027]; // always recurses\n ...\nif (!isSequence \u0026\u0026 !isOptions) {\n if (m.post.match(/,(?!,).*\\}/)) {\n str = m.pre + \u0027{\u0027 + m.body + escClose + m.post;\n return expand_(str, max, true); // restart \u2014 `post` discarded\n }\n return [str];\n}\n```\n\nFor input like a{},{},\u2026, the first {} is non-expanding, so control reaches the {a},b} rewrite branch - but `expand_` has already recursed into post over the entire remaining tail, only to throw the result away.\nEach level therefore spawns two recursive expansions over essentially the same remaining work: `T(n) = 2\u00b7T(n\u22121) \u21d2 O(2\u207f)`.\n\nThe max option does not mitigate this: max only bounds the output-building loops; neither the post recursion nor the rewrite recursion consults it.\n \nMeasured on 5.0.6:\n\n| groups (n) | input bytes | time |\n|---|---|---|\n| 20 | 60 | 130 ms |\n| 24 | 72 | 1.9 s |\n| 26 | 78 | 7.8 s |\n| 30 (PoC) | 90 | ~2 min |\n\n### Proof of concept\n```js\nconst { expand } = require(\u0027brace-expansion\u0027);\n// 30 non-expanding groups, ~90 bytes \u2014 blocks for minutes:\nexpand(\u0027a{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{},{}\u0027);\n```\n\n### Impact\n\nAny application that passes attacker-influenced strings to brace-expansion.expand() - directly or transitively via minimatch/glob brace patterns - can be driven into a multi-minute-to-indefinite CPU hang by a tiny request, denying service on that thread/process.\n\n### Remediation\n\nUpgrade to a patched release. The fix:\n1. Defers computing post until after the early-return branches (and computes it locally in the $-suffix branch), so post is only expanded when a brace set actually expands and the value is used. This alone removes the exponential.\n1. Converts the {a},b} rewrite from recursion to an in-function loop, so a long run of rewrites cannot grow the call stack.\n\nVerified: the PoC drops from ~2 min to 0.55 ms, 5,000 groups complete in ~344 ms, and output is identical to 5.0.6 across a behavioral-equivalence suite (sequences, padding, $-prefix, a{},b}c, {},a}b, x{{a,b}}y, etc.). Post-fix complexity is ~O(n\u00b2) on this input class - acceptable for the security fix; a linear rewrite can be a non-urgent follow-up.\n\nIf immediate upgrade isn\u0027t possible, avoid passing untrusted input to expand() / glob brace patterns, or run such expansion under a timeout/worker.",
"id": "GHSA-3jxr-9vmj-r5cp",
"modified": "2026-07-20T20:51:10Z",
"published": "2026-07-20T20:51:09Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/security/advisories/GHSA-3jxr-9vmj-r5cp"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-13149"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/pull/122"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/pull/123"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/commit/835d6be91201122d9adffb0c0c8c094189ace265"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/commit/c7e33ec13ac1a684c116720843ce24e208611754"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/commit/d74e63030c012e3b7ae81657b8d665619cd51b95"
},
{
"type": "PACKAGE",
"url": "https://github.com/juliangruber/brace-expansion"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/releases/tag/v1.1.16"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/releases/tag/v2.1.2"
},
{
"type": "WEB",
"url": "https://github.com/juliangruber/brace-expansion/releases/tag/v5.0.7"
},
{
"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:L",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P/S:N/AU:Y/R:U/V:D/RE:M/U:Amber",
"type": "CVSS_V4"
}
],
"summary": "brace-expansion: DoS via exponential-time expansion of consecutive non-expanding {} groups"
}
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
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.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
Loading timeline…
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.