CVE-2026-118654 in Echo
Summary
by MITRE • 10/28/2026
Echo is a Go web framework. Prior to 4.16.0 and 5.4.0, Echo's static file handlers can normalize dot segments after route matching and serve a file through a public static route even though the corresponding direct path is protected by route-level middleware. An unauthenticated attacker can read files that an application intended to protect with route-level middleware, when those files are also reachable through a static filesystem mount after path normalization. This vulnerability is the result of an incomplete fix for CVE-2026-55677. This issue is fixed in 4.16.0 and 5.4.0.
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Analysis
by VulDB Data Team • 10/28/2026
The Echo web framework, a popular high-performance HTTP server written in Go, contains a critical path traversal vulnerability that allows unauthenticated attackers to bypass route-level security controls. This flaw specifically affects versions prior to 4.16.0 for the v4 branch and prior to 5.4.0 for the v5 branch. The core issue lies in how the framework handles static file serving relative to dynamic route matching and middleware execution order. When a request is received, Echo processes it through its router to determine which handler should execute based on the URL path. However, when the application also serves files from a public directory using a static filesystem mount, there exists an inconsistency in how paths are normalized before access control checks are applied versus how they are resolved for file serving.
The technical flaw stems from an incomplete fix for CVE-2026-55677. In previous iterations of this vulnerability class, attackers could exploit path normalization to escape intended directories or bypass authentication middleware by manipulating dot segments such as .. in the URL path. The framework's static file handler normalizes these dot segments after route matching has already occurred but potentially before strict access control policies tied to specific dynamic routes are fully enforced for that normalized path. Consequently, if an application protects a sensitive resource via a specific route with authentication middleware, and simultaneously serves files from a directory containing those resources through a separate static mount point, the normalization process can resolve the maliciously crafted URL to a protected file location without triggering the protective middleware associated with the original dynamic route.
This architectural inconsistency results in a significant operational impact where sensitive data becomes accessible to unauthenticated users. An attacker does not need valid credentials or tokens because they are circumventing the authentication layer entirely by exploiting the static file serving mechanism instead of interacting directly with the protected API endpoint. By constructing URLs that include normalized path sequences, such as /static/../../protected/sensitive-file.txt, an attacker can read files that were intended to be restricted to authenticated users only. This leads to unauthorized data disclosure, which may expose confidential business information, user personal data, or internal system configurations depending on the application's file structure and static directory mapping.
From a classification perspective, this vulnerability aligns with CWE-284 Improper Access Control, as it involves bypassing intended access restrictions through path manipulation. It also relates to CWE-22 Path Traversal: Reading Files from Outside the Restricted Directory, given that the attacker leverages normalized paths to access files outside their expected public scope or beyond middleware protections. In terms of MITRE ATT&CK tactics, this behavior corresponds to T1083 File and Directory Discovery, where an adversary explores the file system structure to locate sensitive information, and potentially T1530 Data from Information Repositories if the accessed files contain structured data stores.
To mitigate this vulnerability, organizations must upgrade Echo to version 4.16.0 or later for v4 users, or version 5.4.0 or later for v5 users. These releases address the incomplete fix by ensuring that path normalization and access control checks are applied consistently across both dynamic route handlers and static file serving mechanisms. Until an upgrade is feasible, developers should implement additional defensive measures such as validating input paths strictly before any processing occurs, avoiding direct mapping of sensitive directories to public static routes, or implementing custom middleware that explicitly validates the final resolved physical path against a whitelist of allowed resources regardless of how it was reached via URL normalization. Regular security audits and penetration testing focusing on path traversal scenarios are recommended to identify similar implementation flaws in web frameworks.