CVE-2026-49473 in Authorization for Expressjs
Summary
by MITRE • 08/13/2026
@cedar-policy/authorization-for-expressjs is an open-source Express.js middleware that integrates Cedar authorization into Express applications by mapping HTTP requests to Cedar actions and evaluating authorization policies before allowing requests to proceed. Versions prior to 0.3.0 have an issue where, under certain circumstances, the middleware matches incoming requests against Cedar action mappings using req.originalUrl, which includes the query string, while Express routes requests using only the path component. The middleware uses req.originalUrl to match incoming requests against Cedar action mappings. In Express, req.originalUrl includes the query string, while route matching uses only the path. This creates a divergence between what Cedar authorizes and what Express executes. When an application defines separate actions for overlapping path prefixes with different authorization requirements (for example, GET /users for listing all users with admin-only access, and GET /users/{id} for retrieving a single user with any authenticated user access), an actor can append a query string to bypass the more restrictive policy. Sending GET /users/?x=1 causes the middleware to match against /users/{id} (with id parameter set to ?x=1) and evaluate the less restrictive action, while Express routes the request to the /users list handler. This allows inappropriate access to the more restrictive endpoint. This issue has been addressed in version 0.30. Some workarounds are available. Validate and sanitize incoming request paths before they reach the authorization middleware. Ensure that applications do not rely solely on the middleware for authorization when defining multiple actions on overlapping path prefixes with different permission levels.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability in cedar-policy/authorization-for-expressjs versions prior to 0.3.0 represents a critical authorization bypass flaw that stems from a fundamental mismatch between how HTTP request paths are processed by Express.js and how Cedar policy evaluation occurs within the middleware. This divergence creates a scenario where the authorization decision is made based on a different path component than what the application actually executes, leading to potentially severe security implications.
The technical root cause of this vulnerability lies in the inconsistent handling of URL components between Express.js routing mechanisms and the Cedar authorization middleware. When Express.js processes incoming requests, it uses req.originalUrl which includes the full URL including query parameters for route matching purposes. However, the cedar middleware incorrectly relies on req.originalUrl to map requests to Cedar action definitions, creating an inconsistency where the path component used for authorization evaluation differs from the path that Express actually executes. This mismatch allows malicious actors to manipulate request URLs by appending query strings to bypass intended access controls.
This vulnerability directly maps to CWE-284 Access Control Bypass and aligns with ATT&CK technique T1078 Valid Accounts, as it enables unauthorized access through manipulation of request parameters rather than legitimate credential compromise. The impact is particularly severe when applications define overlapping path prefixes with different authorization requirements, such as a scenario where GET /users requires admin privileges while GET /users/{id} allows authenticated users. The middleware's incorrect path resolution causes the more permissive policy to be evaluated instead of the restrictive one, allowing unauthorized access to restricted endpoints.
The operational implications extend beyond simple privilege escalation, as this flaw can enable data exfiltration, privilege escalation, and unauthorized system access depending on the specific authorization policies in place. Attackers can exploit this by crafting requests with specific query string parameters that cause the middleware to match against less restrictive action definitions while Express routes the actual execution to more restricted endpoints. This creates a false sense of security where applications appear to be properly protected but contain a backdoor through the path resolution inconsistency.
Organizations using affected versions should immediately upgrade to 0.3.0 or later to remediate this vulnerability, as no effective workarounds exist that can fully address the core architectural issue without modifying the middleware behavior itself. The recommended mitigations include implementing additional validation layers before authorization middleware execution and ensuring that applications do not rely solely on this middleware for critical access controls when dealing with overlapping path prefixes. Security teams should also conduct thorough reviews of their authorization policies to identify any potential paths that could be exploited through similar mechanisms, particularly focusing on endpoint definitions with overlapping prefixes and varying permission levels.