CVE-2026-55677 in echo
Summary
by MITRE • 06/26/2026
Echo is a Go web framework. Prior to 4.15.3 and 5.2.0, Echo's router and static file handler disagree on URL path decoding. The router matches routes using the raw encoded path (preserving %2F as-is), while StaticDirectoryHandler unescapes %2F to / before resolving filesystem paths. This allows an attacker to bypass route-level access controls and read static files without authorization. This vulnerability is fixed in 4.15.3 and 5.2.0.
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Analysis
by VulDB Data Team • 06/26/2026
The vulnerability in the Echo Go web framework stems from a fundamental inconsistency in how the router and static file handler process URL path encoding, creating a security gap that can be exploited to bypass access controls. This issue affects versions prior to 4.15.3 and 5.2.0 where the routing mechanism operates on raw encoded paths while the static file handler performs URL decoding before filesystem resolution. The core technical flaw manifests when paths containing encoded forward slashes %2F are processed through different code paths, leading to inconsistent behavior between route matching and file system access. When an attacker crafts a request with encoded path segments, the router matches against the original encoded path while the static file handler resolves the decoded version, creating a mismatch that allows unauthorized file access.
This inconsistency creates a significant operational impact as it enables attackers to traverse directory structures and access protected static files that should be restricted by route-level access controls. The vulnerability specifically exploits the difference in how %2F sequences are handled where the router preserves these encoded characters while the static handler converts them to actual forward slashes during path resolution. This discrepancy allows malicious actors to construct requests that match valid routes but resolve to unintended filesystem locations, effectively bypassing authorization mechanisms. The attack vector becomes particularly dangerous when combined with directory traversal patterns, as demonstrated by the ability to access files outside of intended directories through carefully crafted encoded paths.
The vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and represents a classic case of inconsistent input handling that leads to privilege escalation. From an ATT&CK perspective, this maps to T1083 (File and Directory Discovery) and T1566 (Phishing) as attackers can discover and access sensitive files through unauthorized paths. The fix implemented in versions 4.15.3 and 5.2.0 addresses the root cause by ensuring consistent path handling between the router and static file handler, normalizing URL decoding behavior across both components. Organizations should immediately upgrade to these patched versions as the vulnerability represents a critical security risk that could allow unauthorized access to sensitive static files and directory structures. Additionally, implementing proper input validation and path normalization at multiple layers of application architecture can help prevent similar inconsistencies in other components.
The broader implications extend beyond this specific framework as it highlights the importance of consistent URL handling across web application components. This vulnerability demonstrates how seemingly minor implementation differences in path processing can create substantial security gaps that affect the entire application security posture. Security teams should conduct thorough audits of their web frameworks and applications to identify similar inconsistencies in path handling, URL decoding, and access control enforcement mechanisms. The remediation process requires not only updating the framework but also ensuring that all static file serving components maintain consistent behavior with routing logic to prevent future exploitation attempts.