8.2 High

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

CVE-2026-118262

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…

Assessment

CVSS: 8.2 (v4.0)
Severity: High
EPSS: 0.00302% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 23 October 2026
Last updated: 28 October 2026
Affected: go · github.com/labstack/echo/v4, github.com/labstack/echo/v5
Weakness: CWE-772

CVSS vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

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