CVE-2026-84376 in Astro
Summary
by MITRE • 09/02/2026
Astro is a web framework for content-driven websites. Prior to 7.2.4, Astro stripped a configured non-root base path from request pathnames using a string-prefix check without verifying a path-segment boundary. With base "/app", a request to "/appX/admin" resolved internally to the protected "/admin" route while middleware observed "/appX/admin" in context.url.pathname. In applications that authorize base-prefixed routes by inspecting context.url.pathname, an unauthenticated remote attacker could bypass pathname-based middleware authorization and reach protected routes. This issue is fixed in version 7.2.4.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability identified in the Astro web framework prior to version 7.2.4 represents a critical path traversal logic error that undermines security controls relying on URL prefix matching for access control. Astro, designed primarily as a modern static site generator and web framework for content-driven websites, utilizes middleware architectures where developers often implement authorization checks based on the request URI. The core technical flaw lies in how the framework processes configured base paths during internal routing resolution. When an application specifies a non-root base path, such as /app, Astro is intended to strip this prefix from incoming request URLs before passing them to the underlying router logic. However, the implementation employed a naive string-prefix check rather than validating that the stripped portion corresponds to a complete URL segment boundary. This means the framework did not verify whether the character immediately following the base path was a forward slash or represented the end of the string, which is required for valid pathname segmentation in standard URI syntax.
This lack of strict boundary verification allows an attacker to craft malicious request URIs that appear to contain the authorized base prefix but actually resolve to protected internal routes after stripping occurs. For instance, if the configured base path is /app and a middleware layer checks whether context.url.pathname starts with /app/admin to grant access, an unauthenticated remote attacker can send a request to /appX/admin. Because the string /appX begins with the substring /app, the framework incorrectly strips it, resolving internally to the protected route /admin. Crucially, while the internal router processes this as a valid match for /admin, the middleware context retains the original unmodified pathname /appX/admin in its URL object. This discrepancy creates a state where the authorization logic sees an unauthorized path that appears authorized due to the prefix check failure, or conversely, allows bypassing checks if the middleware relies on the internal routing result while failing to validate the external input properly.
The operational impact of this vulnerability is significant for applications implementing pathname-based authentication and authorization schemes. Attackers can exploit this flaw to bypass access controls without needing valid credentials or tokens, effectively gaining unauthorized access to administrative interfaces, sensitive data endpoints, or other protected resources that were intended to be restricted by base path configuration. This type of issue aligns with CWE-284 Improper Access Control, specifically reflecting failures in enforcing security policies through insufficient validation of input boundaries. Furthermore, it relates to CWE-697 Incorrect Comparison during access control checks, as the framework fails to correctly compare the intended scope against the actual request path due to loose string matching rules. From a threat modeling perspective using MITRE ATT&CK, this vulnerability facilitates Initial Access and Privilege Escalation techniques by allowing attackers to bypass authentication mechanisms through URL manipulation, specifically leveraging Path Traversal or Obfuscated File/Directory access patterns to reach restricted areas of an application.
To mitigate this risk, organizations running Astro versions prior to 7.2.4 must upgrade immediately to version 7.2.4 or later, where the path stripping logic has been corrected to enforce strict segment boundary validation. This ensures that only requests with exact base path prefixes followed by a delimiter are processed correctly, preventing ambiguous matches like /appX from being treated as valid instances of /app. For applications unable to upgrade immediately due to dependency constraints, developers should implement additional defensive measures in their middleware layers. These include manually validating the request URL against strict regular expressions that enforce segment boundaries rather than relying solely on substring checks or framework-provided path stripping for security decisions. Additionally, implementing comprehensive logging and monitoring for anomalous URI patterns can help detect exploitation attempts of this vulnerability before they result in unauthorized access.