Echo (V4 < 4.16.1) - CraftedSignal Threat Feedhttps://feed.craftedsignal.io/products/echo-v4--4.16.1/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioFri, 23 Oct 2026 21:44:59 +0000https://feed.craftedsignal.io/favicon-32x32.pngCraftedSignal Threat Feedhttps://feed.craftedsignal.io/3232https://feed.craftedsignal.io/favicon.svgLabstack Echo: Proxy middleware WebSocket upgrade bypasshttps://feed.craftedsignal.io/briefs/2026-10-echo-websocket-bypass/Fri, 23 Oct 2026 21:44:59 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-10-echo-websocket-bypass/The Labstack Echo web framework Proxy middleware incorrectly establishes a raw tunnel for WebSocket upgrades before validating upstream responses, allowing subsequent HTTP requests to bypass route-level authentication and authorization.The Proxy middleware in Labstack Echo (v4 and v5) fails to validate if an upstream server successfully upgrades to a WebSocket connection. When an upstream server rejects a WebSocket upgrade request but keeps the underlying TCP connection open, Echo incorrectly maintains a raw tunnel. This state causes subsequent HTTP requests on that same connection to be forwarded directly to the upstream service, bypassing any Echo-level router logic or middleware (e.g., authentication, authorization).

Attack Chain

  1. Attacker identifies a proxy route in an Echo-based application.
  2. Attacker sends a WebSocket upgrade request (HTTP GET with Connection: Upgrade, Upgrade: websocket) to the proxy route.
  3. The target upstream service receives the request, determines it cannot upgrade, and returns a standard HTTP response (e.g., 400 or 403) while keeping the connection alive.
  4. Echo's Proxy middleware erroneously promotes the connection to a raw tunnel upon receiving the upgrade initiation, failing to confirm the upstream's non-101 response status.
  5. Attacker sends subsequent unauthorized HTTP requests over the existing, now-tunneling connection.
  6. The proxy forwards these requests directly to the upstream, bypassing route-level controls implemented in the Echo layer.

Impact

Unauthorized access to upstream resources that rely on Echo-level authentication or authorization. The bypass does not provide arbitrary-host proxying and relies on existing upstream reachability.

Recommendation

  • Upgrade Echo to v4.16.1 or v5.4.1 immediately to implement upstream response validation.
  • If immediate patching is not possible, enforce independent authentication and authorization checks at the upstream resource level.
  • Implement request filtering at the perimeter or load balancer to block WebSocket upgrade requests if they are not explicitly required for specific routes.
]]>criticaladvisory