high · 8.2 Patched

Echo: WebSocket proxy can retain connections and handlers after client disconnect

GHSA-9969-6676-49h5 · published 23 Oct 2026

How serious is it

  • Severity: high, CVSS score 8.2 out of 10.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by GHSA-9969-6676-49h5?

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Who is affected

  • github.com/labstack/echo/v4 (Go) >= 4.15.0, < 4.16.1
  • github.com/labstack/echo/v5 (Go) >= 5.0.0, < 5.4.1

How to check

  1. Run go list -m github.com/labstack/echo/v4 in your project to see the installed version, including copies pulled in by other packages.
  2. Run go list -m github.com/labstack/echo/v5 in your project to see the installed version, including copies pulled in by other packages.
  3. Or paste your lockfile into the checker: it lists every package with a known vulnerability, this one included.

How to fix

Copies a prompt for Claude Code, Cursor or Codex: it checks your lockfiles for this and upgrades it.
  1. On >= 4.15.0, < 4.16.1: Upgrade github.com/labstack/echo/v4 to 4.16.1 or later, commit the lockfile and redeploy.
  2. On >= 5.0.0, < 5.4.1: Upgrade github.com/labstack/echo/v5 to 5.4.1 or later, commit the lockfile and redeploy.
  3. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

## Impact Echo's Proxy middleware could retain a handler, copy goroutines and network connections after a WebSocket client disconnected if the upstream kept its connection open. The raw proxy waited for both copy directions to finish without reliably closing the other connection when one direction ended. Rejected upgrade responses with HTTP keep-alive were one way to trigger this behavior. Repeated connections can accumulate resources and cause denial of service. The impact depends on the proxy route's accessibility, upstream behavior and configured connection deadlines. This is a medium-severity resource-retention issue; no confidentiality or integrity impact is claimed. ## Affected versions and patch Affected versions are v4.15.0 through v4.16.0 and v5.0.0 through v5.4.0. The regression was introduced by commit e2133320c7, merged in #2852. Upgrade to [v4.16.1](https://github.com/labstack/echo/releases/tag/v4.16.1) or [v5.4.1](https://github.com/labstack/echo/releases/tag/v5.4.1). The patch uses Go's HTTP reverse proxy, preserves ordinary HTTP handling for rejected upgrades, and closes both sides of a WebSocket tunnel when either direction ends. It also covers an upstream that receives client EOF but deliberately keeps its side open. Fix commits: [v4](https://github.com/labstack/echo/commit/3fb0ba7e17645bb65611e2a08875d0a2f65c421f), [v5](https://github.com/labstack/echo/commit/1855061e572ae9dab727c811d8382f266bfbaaec). ## Workarounds Disable WebSocket proxy routes until upgrading, or apply bounded connection lifetimes and resource limits at the frontend and upstream. Server idle timeouts alone may not cover hijacked WebSocket connections. ## Credits Reported by @irisitymichaelgrundberg.

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References

Merged from GitHub Advisory Database, OSV. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON

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