CVE-2026-41248
CRITICALCVE-2026-41248 is a critical-severity (CVSS 9.1) CWE-436 vulnerability in @clerk/nextjs. O3 Security confirms whether CVE-2026-41248 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Official Clerk JavaScript SDKs: Middleware-based route protection bypass
Blast Radius
@clerk/nextjs📦@clerk/nuxt📦@clerk/astro📦@clerk/shared📦@clerk/nextjs📦@clerk/nextjs📦@clerk/nuxt📦@clerk/astro+3 moreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
Clerk JavaScript is the official JavaScript repository for Clerk authentication. createRouteMatcher in @clerk/nextjs, @clerk/nuxt, and @clerk/astro can be bypassed by certain crafted requests, allowing them to skip middleware gating and reach downstream handlers. This vulnerability is fixed in @clerk/astro 1.5.7, 2.17.10, and 3.0.15; @clerk/nextjs 5.7.6, 6.39.2, and 7.2.1; @clerk/nuxt 1.13.28 and 2.2.2; and @clerk/shared 2.22.1, 3.47.4, anc 4.8.1
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @clerk/nextjs | ≥ 5.0.0&&< 5.7.6 | 5.7.6 |
| 📦npm | @clerk/nuxt | ≥ 1.1.0&&< 1.13.28 | 1.13.28 |
| 📦npm | @clerk/astro | ≥ 0.0.1&&< 1.5.7 | 1.5.7 |
| 📦npm | @clerk/shared | ≥ 2.20.17&&< 2.22.1 | 2.22.1 |
| 📦npm | @clerk/nextjs | ≥ 6.0.0-snapshot.vb87a27f&&< 6.39.2 | 6.39.2 |
| 📦npm | @clerk/nextjs | ≥ 7.0.0&&< 7.2.1 | 7.2.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @clerk/nextjs. 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 @clerk/nextjs to 5.7.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41248 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 CVE-2026-41248 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 CVE-2026-41248. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41248 in your dependencies?
O3 detects CVE-2026-41248 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.