Nuxt 4.x Route Parameter Confusion Vulnerability (CVE-2026-120309) Analysis & Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTNuxt versions from 4.6.0 before 4.6.2
Attackers can cause a discrepancy between Nuxt helpers and the h3 router by sending paths with an encoded question mark (%3F), potentially bypassing authorization checks to access unauthorized resources.
Immediately upgrade the Nuxt package to a secure version (4.6.2 or higher).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade your Nuxt dependency to version 4.6.2 or higher to apply the official security patch. Run the appropriate command for your package manager:
# For npm users
npm install nuxt@4.6.2 --save-exact
# For yarn users
yarn add nuxt@4.6.2 --exact
# For pnpm users
pnpm add nuxt@4.6.2 --save-exact2. Temporary Workaround & Hardening Configuration
If an immediate upgrade is not feasible, implement a server-side middleware to intercept and reject incoming requests containing encoded question marks (%3F or %3f) in the path:
// server/middleware/block-encoded-query.ts
export default defineEventHandler((event) => {
const rawUrl = event.node.req.url || '';
if (rawUrl.includes('%3F') || rawUrl.includes('%3f')) {
throw createError({
statusCode: 400,
statusMessage: 'Bad Request: Encoded query characters are prohibited in path.'
});
}
});3. Log Audit & IoC Verification Commands
Verify your current Nuxt installation version and scan your web server access logs for potential exploitation attempts using the following commands:
# 1. Check the installed Nuxt version in your project
npm list nuxt
# 2. Scan Nginx or application access logs for encoded question marks (%3F)
grep -i '%3F' /var/log/nginx/access.log | grep -E 'GET|POST'Scan Your Repositories for Transitive Vulnerable Dependencies in 30 Seconds
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2026-120309) is a route parameter confusion issue residing in Nuxt's getRouterParam and getRouterParams helper utilities. The root cause stems from an inconsistency (CWE-436) in how the underlying HTTP framework h3 matches routes compared to how Nuxt's internal helpers parse parameters when the request path contains an encoded question mark (%3F). This discrepancy leads to different parameter values being resolved for the same request.
2. Exploitation Mechanics & Attack Scenario
An attacker crafts a malicious HTTP request containing an encoded question mark (%3F) within the URL path (e.g., /api/user/123%3Fadmin). When processed, authorization checks utilizing the Nuxt helper getRouterParam resolve to one value (e.g., 123), passing the security validation. However, the actual resource selection logic utilizing event.context.params resolves to a different value (e.g., admin). This parameter mismatch allows the attacker to bypass access controls and retrieve unauthorized resources.
3. Infrastructure & Business Impact
Although rated with a CVSS score of 3.7 (Low), the real-world impact highly depends on the application's authorization architecture. In enterprise applications where access control decisions rely on Nuxt's built-in helpers while data fetching relies on raw context parameters, this vulnerability can lead to unauthorized data exposure, privilege escalation, and business logic bypass.
Official Vendor Advisories & References
Nuxt from 4.6.0 before 4.6.2 contains a route parameter confusion vulnerability in getRouterParam and getRouterParams that lets attackers return a parameter value different from the one h3 matched by sending paths containing an encoded question mark (%3F). Attackers can craft requests where authorization checks use the Nuxt helper value while resource selection uses event.context.params, allowing access to unauthorized resources.
Frequently Asked SecOps Questions (CVE-2026-120309)
FAQQ1. How critical is CVE-2026-120309 and is it actively exploited in the wild?
CVE-2026-120309 is rated CVSS 3.7 (LOW) with a 30-day EPSS exploitation probability of 0.2%. Organizations running affected versions should prioritize patching based on network exposure.
Q2. Which vendors and products are affected by CVE-2026-120309?
Primary impacted vendors include nuxt across nuxt. Scope summary: Nuxt versions from 4.6.0 before 4.6.2
Q3. What temporary mitigations or workarounds exist for CVE-2026-120309 before patching?
[Mitigation] Immediately upgrade the Nuxt package to a secure version (4.6.2 or higher). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2026-120309
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