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CVE-2026-84376: CVE-2026-84376: Authorization Bypass via Missing Path-Segment Boundary Validation in Astro

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CVE-2026-84376: Authorization Bypass via Missing Path-Segment Boundary Validation in Astro

Vulnerability ID: CVE-2026-84376
CVSS Score: 6.3
Published: 2026-09-08

An authorization bypass vulnerability exists in the Astro web framework prior to version 7.2.4. When configured with a non-root base path, Astro's routing engine stripped the base path from incoming request URLs using an insecure prefix-match check without verifying path-segment boundaries. This created a path parser differential between user-defined middleware and the internal router. An unauthenticated attacker could bypass route-based authorization checks to access administrative or privileged endpoints by altering the path prefix segment.

TL;DR

Astro prior to 7.2.4 allowed attackers to bypass path-based authorization middleware via a partial string matching flaw when stripping custom base paths (e.g., /appX/admin resolved to /app/admin but bypassed middleware looking for /app/admin).

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-187 (Partial String Comparison)
  • Attack Vector: Network (AV:N)
  • CVSS Score: 6.3 (Medium)
  • EPSS Score: 0.00407 (Percentile: 33.98%)
  • Impact: Authorization Bypass
  • Exploit Status: PoC available (Unit test validation)
  • KEV Status: Not Listed in CISA KEV

Affected Systems

  • Astro web application deployments utilizing a custom, non-root base path and relying on pathname-based authorization middleware.
  • astro: < 7.2.4 (Fixed in: 7.2.4)

Code Analysis

Commit: 05763a0

Consolidate and secure path stripping logic in stripRequestBase to prevent partial string matching bypass.

Mitigation Strategies

  • Upgrade the core Astro framework to version 7.2.4 or newer.
  • Implement runtime validation inside middleware to block path-segment suffix bypass attempts if immediate patching is not possible.

Remediation Steps:

  1. Open the project configuration package.json.
  2. Update the 'astro' dependency version to '^7.2.4'.
  3. Execute your package manager's install command (e.g., npm install or pnpm install) to download and apply the patch.
  4. Verify the configured 'base' path properties inside astro.config.mjs.
  5. Deploy the updated application and run integration tests using suffix-altered request paths to verify that they now return a 404 response.

References

Read the full report for CVE-2026-84376 on our website for more details including interactive diagrams and full exploit analysis.

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