Executive Summary

CVE-2026-55677 is a vulnerability in the Echo web framework for Go, affecting versions prior to 4.15.3 and 5.2.0. The issue arises because the router and the static file handler process URL paths differently. The router matches routes using the raw encoded path, preserving encoded slashes (%2F), while the static file handler decodes %2F into a forward slash (/) before accessing filesystem paths.

This inconsistency allows an attacker to bypass route-level access controls by encoding slashes in URLs. For example, an attacker could request a URL like /admin%2Fsecret.txt to bypass authentication middleware protecting /admin/* routes, while the static file handler resolves this to admin/secret.txt on disk, granting unauthorized access to static files.

Useful 0 Not Useful 0

Impact Analysis

This vulnerability can lead to unauthorized disclosure of sensitive static files on a server using the affected Echo versions. Attackers do not need any privileges or user interaction to exploit this issue, making it easier to access protected files by bypassing route-level access controls.

The impact is significant because it can expose confidential information stored as static files, potentially leading to data breaches or leakage of sensitive data.

Useful 0 Not Useful 0

Detection Guidance

This vulnerability can be detected by monitoring HTTP requests for encoded slashes (%2F) in URLs that access static files, especially in routes protected by authentication middleware.

For example, an attacker might request a URL like /admin%2Fsecret.txt to bypass route-level access controls.

You can use network monitoring tools or web server logs to search for such encoded slash patterns in URLs.

• Use grep or similar tools on web server logs to find requests containing '%2F':
• grep '%2F' /path/to/access.log
• Use curl or wget to test if encoded slashes bypass route protections:
• curl -i http://yourserver/admin%2Fsecret.txt

Useful 0 Not Useful 0

Mitigation Strategies

The immediate step to mitigate this vulnerability is to upgrade the Echo web framework to a fixed version.

• Upgrade Echo to version 4.15.3 or later if using v4.
• Upgrade Echo to version 5.2.0 or later if using v5.

These versions contain patches that fix the inconsistency between the router and static file handler in URL path decoding.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability allows an attacker to bypass route-level access controls and read static files without authorization. Such unauthorized data disclosure can lead to exposure of sensitive or personal information.

Exposure of sensitive data due to this vulnerability could result in non-compliance with data protection regulations and standards such as GDPR and HIPAA, which require strict access controls and protection of personal and health information.

Useful 0 Not Useful 0