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Security Digest · Critical advisory (no CVE assigned)

GHSA-cxf3-9h37-7rr8: Echo: Rejected WebSocket upgrades can bypass Echo route-level access controls

Impact Echo's Proxy middleware selected a raw tunnel when the client requested a WebSocket upgrade, before validating whether the configured upstream accepted it.

CVSS 9.1 Critical GitHub-reviewed · critical

Published By erroneo.us Security DeskSeen in the digest for Oct 23, 2026

Should you act?

  • Only if you depend on one of the packages below, directly or transitively, in a vulnerable version. Check your lockfile with govulncheck ./....
  • No CVE has been assigned, so it will not appear in CVE-based scanners that ignore GitHub advisories. npm audit, pip-audit and Dependabot do read GitHub advisories.

Affected packages

EcosystemPackageVulnerableFirst fixed
Gogithub.com/labstack/echo/v4>= 4.0.0, < 4.16.14.16.1
Gogithub.com/labstack/echo/v5>= 5.0.0, < 5.4.15.4.1

Details

Impact

Echo's Proxy middleware selected a raw tunnel when the client requested a WebSocket upgrade, before validating whether the configured upstream accepted it. If the upstream returned an ordinary HTTP response and kept the connection alive, subsequent HTTP requests on that connection were forwarded directly to the same upstream without passing through Echo's router or route-specific middleware.

This can bypass authentication or authorization enforced only at Echo's routes. Exploitation requires an accessible proxy route, an upstream that rejects the upgrade without closing the connection, and a target resource on that upstream without independent authorization. The issue does not provide arbitrary-host proxying or bypass the upstream's own authentication.

Affected versions and patch

The raw proxy implementation is present throughout the v4 and v5 release lines up to v4.16.0 and v5.4.0. Runtime reproductions confirmed v4.15.0, v4.16.0, v5.0.0 and v5.4.0; source history also shows the missing upgrade-response validation in v4.0.0.

Upgrade to v4.16.1 or v5.4.1. The patch routes WebSocket upgrades through Go's HTTP reverse proxy and enters a tunnel only after a valid upstream upgrade response. Rejected upgrades remain ordinary HTTP requests.

Fix commits: v4, v5.

Workarounds

CVSS: 9.1 (v4.0) CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Sources and references

  1. GitHub Advisory GHSA-cxf3-9h37-7rr8 github.com
  2. github.com github.com
  3. github.com github.com
  4. github.com github.com
  5. github.com github.com
  6. github.com github.com

Critical Go advisories · Today’s Security Digest