Echo Go Framework Patched for Critical WebSocket Access Control Bypass Vulnerability
TL;DR
Maintainers of the LabStack Echo Go framework disclosed a critical access control bypass vulnerability tracked as CVE-2026-118264 (CVSS v4.0: 9.1). The flaw allows unauthenticated attackers to bypass route-level authentication and authorization middleware via rejected WebSocket upgrade requests. Developers must update their Go dependencies to Echo v4.16.1 or v5.4.1 immediately.
Why It Matters
Echo is a minimalist, high-performance Go web framework with over 32,800 stars and 4,900 forks on GitHub. While exact counts of vulnerable production deployments are not specified in the advisory, thousands of microservices and API gateways rely on the Echo Go framework to route and authenticate HTTP traffic.
Reported by security researcher Duodum, this flaw exposes internal backend endpoints that rely solely on Echo’s route-level middleware for protection. Currently, no public proof-of-concept exploit code has been published, and no active exploitation in the wild has been confirmed.
How the Attack Works
According to the security advisory, the vulnerability stems from inconsistent HTTP request handling (CWE-444) and incorrect authorization (CWE-863) in Echo’s Proxy middleware.
Raw Tunnel Smuggling via Rejected Upgrades
When a client sends a WebSocket upgrade request to a proxied route, Echo’s Proxy middleware immediately selects a raw network tunnel before verifying whether the configured upstream server accepts the protocol switch. If the upstream server rejects the WebSocket upgrade with a standard HTTP response and keeps the connection alive, the raw tunnel remains open.
Consequently, any subsequent HTTP requests sent over that same connection are forwarded directly to the upstream server without passing through Echo’s router or route-specific authentication middleware. While this does not enable arbitrary-host proxying or bypass the upstream server’s own authentication checks, it bypasses all access controls enforced exclusively at Echo’s routes.
Affected Versions
This Echo Go framework vulnerability affects all v4 and v5 releases prior to the patched builds, specifically versions from 4.0.0 before 4.16.1 and from 5.0.0 before 5.4.1. Versions v4.16.1 and v5.4.1 are unaffected.
Patch and Mitigation Steps
LabStack resolved CVE-2026-118264 in Echo v4.16.1 and v5.4.1 by routing WebSocket upgrades through Go’s standard HTTP reverse proxy and establishing a tunnel only after receiving a valid upstream upgrade response. Developers should upgrade to v4.16.1 or v5.4.1 immediately. If an immediate upgrade is impossible, teams should reject WebSocket upgrade requests before they reach affected proxy routes or enforce independent authorization checks directly on every upstream resource.
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