GHSA-3jxr-9vmj-r5cp is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in brace-expansion. O3 Security confirms whether GHSA-3jxr-9vmj-r5cp is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
brace-expansion: DoS via exponential-time expansion of consecutive non-expanding {} groups
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3jxr-9vmj-r5cp.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-3jxr-9vmj-r5cp plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
brace-expansionnpmDescription
Summary
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:
- 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.
- 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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | brace-expansion | ≥ 3.0.0&&< 5.0.7 | 5.0.7 |
| 📦npm | brace-expansion | all versions | 1.1.16 |
| 📦npm | brace-expansion | ≥ 2.0.0&&< 2.1.2 | 2.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for brace-expansion. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update brace-expansion to 5.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3jxr-9vmj-r5cp is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-3jxr-9vmj-r5cp is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-3jxr-9vmj-r5cp. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A flaw was found in brace-expansion, a widely-used npm package for expanding brace sequences. The expand() function exhibits exponential-time complexity when processing consecutive non-expanding brace groups. An attacker who can supply crafted input to expand(), directly or transitively via minimatch or glob, can…
Frequently Asked Questions
Is GHSA-3jxr-9vmj-r5cp in your dependencies?
O3 detects GHSA-3jxr-9vmj-r5cp across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.