CVE-2026-55677: Echo Web Framework Path Traversal in Static File Handler

Technical summary

Echo's router evaluates routes against the raw, URL-encoded path (treating %2F as a literal sequence), while StaticDirectoryHandler unescapes percent-encoded characters before filesystem resolution. This inconsistency in path normalization allows an attacker to craft requests like /protected%2F..%2F../sensitive.txt that pass router validation but resolve to unauthorized files after decoding. The vulnerability is rooted in CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and affects Echo versions prior to 4.15.3 (v4 branch) and 5.2.0 (v5 branch).

Business impact

Any application using Echo's StaticDirectoryHandler to serve restricted static assets is vulnerable to unauthorized file disclosure. An attacker can read configuration files, source code, private keys, or other sensitive data without authentication. This is particularly dangerous for single-page applications or microservices that rely on Echo's static file serving for non-public content or that have conditional access logic in the router.

Affected systems

Echo web framework versions 4.x prior to 4.15.3 and 5.x prior to 5.2.0. Applications using StaticDirectoryHandler for path-based access control are at highest risk. Those relying exclusively on external reverse proxies or middleware-layer auth may have reduced exposure, depending on configuration.

Exploitability

Exploitation requires no authentication, no special privileges, and no user interaction. An attacker simply crafts HTTP requests with percent-encoded path traversal sequences. The attack surface is the static file serving endpoint itself. No CVSS score downgrades apply; this is a straightforward remote bypass with a CVSS 3.1 score of 7.5 (HIGH).

Remediation

Upgrade Echo to version 4.15.3 or later (v4 users) or 5.2.0 or later (v5 users). Both versions implement consistent path normalization between the router and static file handler. No workarounds are practical without code modification; patching is the only reliable fix.

Patch guidance

For Go projects using Echo as a dependency: update go.mod to reference echo v4.15.3+ or echo v5.2.0+, then run 'go get -u' and 'go mod tidy'. Rebuild and redeploy applications. Verify the upgrade in your build and staging environments before production rollout. Check your go.sum file to confirm the new version is locked.

Detection guidance

Monitor HTTP request logs for patterns like %2F in static file paths, especially combined with ../ or path traversal-like sequences. Analyze access logs for requests to StaticDirectoryHandler endpoints that contain percent-encoded characters. Implement filesystem-level auditing on static file directories to detect unexpected file reads. Source code scanning can identify Echo usage and version pinning to flag vulnerable deployments.

Why prioritize this

HIGH priority. The vulnerability is unauthenticated, requires no user interaction, and directly enables unauthorized file access. While not in the CISA KEV catalog, it poses immediate risk to confidentiality. Any organization serving sensitive static content via Echo should patch urgently.

Risk score, explained

CVSS 3.1 score of 7.5 reflects high attack complexity (network-only, no auth required), high impact on confidentiality (full file disclosure), and no integrity or availability impact. The vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N captures the unauthenticated remote nature and file read capability without system compromise.

Frequently asked questions