CVE-2026-118650 in Echo
Summary
by MITRE • 10/28/2026
Echo is a Go web framework. Prior to 4.16.0 and 5.4.0, a globally mounted middleware.Static instance can interpret an encoded request path differently from Echo's router because the router matches the still-encoded path while the static handler uses the decoded URL.Path. The advisory demonstrates an encoded slash resolving to a file under the static root through the global static middleware, but the source is internally inconsistent about whether a route or group guard protects the corresponding literal path in that global-mount configuration. 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 for Go contains a critical logic flaw related to URL decoding inconsistencies between its routing engine and static file serving middleware, specifically affecting versions prior to 4.16.0 and 5.4.0. This vulnerability arises from the divergent handling of encoded request paths within globally mounted middleware.Static instances. When an HTTP request is received, Echo's router processes the incoming URL path while it remains in its percent-encoded state for route matching purposes. However, the static file handler relies on the decoded version of the URL.Path to determine which files to serve from the filesystem. This discrepancy creates a scenario where the routing layer and the middleware layer interpret the same request differently, leading to potential security bypasses or unauthorized access scenarios that were not anticipated by the framework's default configuration logic.
The operational impact of this vulnerability is significant for applications relying on global static file serving with encoded paths in their URLs. An attacker can craft a malicious HTTP request containing percent-encoded slashes within the path segment intended to locate files under the static root directory. Because the router matches against the encoded string, it may successfully validate and allow the request through initial security guards or route definitions that expect literal characters. Once passed to the middleware.Static handler, the URL is decoded, causing the server to interpret the encoded slash as a directory separator. This allows an attacker to traverse outside of intended boundaries or access files located in subdirectories beneath the static root that were not explicitly exposed by individual routes. The advisory notes internal inconsistencies regarding whether route-level guards protect these paths, suggesting that even with some protective measures, the fundamental decoding mismatch can be exploited if those protections do not account for encoded traversal sequences.
From a classification perspective, this vulnerability aligns closely with CWE-20 Improper Input Validation and CWE-749 Exposed Dangerous Method or Function in certain contexts where input normalization is required before processing. It also relates to path traversal concepts found in CWE-22 Path Traversal: Outside Current Directory With Special Elements Like Dot Slash and Double-Dot Slash, although the mechanism here relies on encoding evasion rather than traditional dot-dot-slash sequences. In terms of offensive security frameworks, this behavior can be mapped to ATT&CK technique T1083 File and Directory Discovery or potentially T1592 Gather Victim Host Information depending on how the accessed files are utilized by an attacker for further exploitation. The core issue is a failure to normalize input consistently across different components of the application stack, allowing encoded characters to bypass logical access controls designed around literal path structures.
Mitigation strategies primarily involve upgrading the Echo framework to version 4.16.0 or 5.4.0 and later, where this inconsistency has been resolved by ensuring that both the router and static middleware operate on consistently decoded paths or apply uniform encoding checks before processing requests. For organizations unable to immediately upgrade, implementing a custom middleware layer that explicitly decodes URL paths early in the request lifecycle can help align routing decisions with file system lookups. Additionally, developers should review their global static middleware configurations to ensure they are not exposing sensitive directories and consider restricting access to specific subdirectories rather than relying solely on broad root mounts. Regular security audits focusing on input validation consistency across web framework components are recommended to prevent similar logic flaws in other parts of the application architecture.