CVE-2026-59731 in astro
Summary
by MITRE • 07/08/2026
Astro is a web framework for content-driven websites. Version 6.4.7 performs authorization decisions on a partially decoded pathname after reaching the iterative URL decoder limit, while later rewrite route matching performs an additional decodeURI() operation and can resolve the request to a protected route. This issue is fixed in version 6.4.8.
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Analysis
by VulDB Data Team • 07/08/2026
This vulnerability affects Astro web framework versions prior to 6.4.8 and represents a critical authorization bypass flaw that stems from inconsistent URL decoding behavior during the request processing pipeline. The vulnerability occurs when the framework reaches its iterative URL decoder limit and performs partial decoding of pathnames, creating a scenario where authorization decisions are made based on partially decoded URLs rather than fully resolved paths. This inconsistency becomes particularly dangerous when subsequent route matching operations perform additional decodeURI() operations that can resolve requests to protected routes that would otherwise be inaccessible.
The technical flaw exploits the difference between the authorization decision point and the route matching point in Astro's request handling architecture, creating a window where malicious actors can manipulate URL encoding to bypass access controls. When a request reaches the iterative decoder limit, the framework stops further decoding operations but continues processing with the partially decoded path. Later during rewrite routing, an additional decodeURI() operation resolves what was previously encoded components, potentially allowing access to resources that should remain protected. This type of vulnerability falls under CWE-287 Authentication Bypass Through User-Controlled Key and can be categorized as a privilege escalation vector within the ATT&CK framework under T1078 Valid Accounts.
The operational impact of this vulnerability is severe as it allows unauthorized users to access protected content, restricted routes, or administrative functions that should only be available to authenticated and authorized personnel. Attackers could potentially exploit this by crafting specifically encoded URLs that, when processed through the framework's inconsistent decoding logic, resolve to protected endpoints while appearing benign during initial authorization checks. The vulnerability affects any Astro application that relies on route-based access controls or authentication mechanisms that depend on URL paths for authorization decisions.
Mitigation strategies should focus on upgrading to Astro version 6.4.8 or later where the issue has been resolved through consistent URL decoding behavior throughout the request processing pipeline. Organizations should also implement additional monitoring and logging of URL patterns, particularly those involving encoded characters, to detect potential exploitation attempts. Security teams should conduct thorough audits of all route-based authorization logic and ensure that access controls are consistently applied regardless of URL encoding states. The fix implemented in version 6.4.8 addresses the root cause by standardizing decoding operations across all stages of request processing, eliminating the discrepancy between authorization decisions and route matching behavior that enabled this vulnerability.