# Echo: Rejected WebSocket upgrades can bypass Echo route-level access controls Advisory record · `GHSA-cxf3-9h37-7rr8` - **Identifiers:** `GHSA-cxf3-9h37-7rr8` · `CVE-2026-118264` · `GO-2026-6839` - **State:** Confirmed - **Severity:** CVSS 9.1 Critical - **Critical:** Yes: CVSS 9+ - **Weakness (CWE):** [CWE-444](https://cwe.mitre.org/data/definitions/444.html) · [CWE-863](https://cwe.mitre.org/data/definitions/863.html) - **Tags:** [HTTP request smuggling](https://agentprime.io/advisories/tag/request-smuggling.md) · [Broken access control](https://agentprime.io/advisories/tag/access-control.md) - **Published:** 23 Oct 2026 - **Updated:** 5 Nov 2026 - **Reviewed by a person:** No Published by the GitHub Advisory Database at 23 Oct 2026, 20:49 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. ## Critical Critical, because: - CVSS score 9.1: 9.0 or more. How we decide what’s critical: ## Affected packages - `github.com/labstack/echo/v4` (Go): affected `>=4.0.0, <4.16.1`; fixed in `4.16.1` - `github.com/labstack/echo/v5` (Go): affected `>=5.0.0, <5.4.1`; fixed in `5.4.1` ## Machine-written summary Summary written by Claude Haiku from the source advisory. Not reviewed by a person. > Echo v4 (>=4.0.0, <4.16.1) and Echo v5 (>=5.0.0, <5.4.1) Proxy middleware can forward HTTP requests to an upstream after a rejected WebSocket upgrade, bypassing route-level authentication or authorization in Echo. An attacker with access to a proxy route whose upstream rejects the upgrade without closing the connection could reach upstream resources that lack their own authorization checks. Upgrade to Echo v4.16.1 or v5.4.1; rejecting WebSocket upgrade requests before they reach affected proxy routes is an alternative workaround. Written 1 Nov 2026. ## Not analysed yet We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check. ## Severity and exploitation - 9.1 Critical, CVSS 4.0: `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`, from CNA (GitHub_M) - **CISA KEV:** Not listed. - **EPSS:** 0.0043, the 37th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days. ## Timeline - 28 Oct 2026, 19:17 UTC: [Confirmed by NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-118264) - 31 Oct 2026, 14:11 UTC: First seen by agentprime - 31 Oct 2026, 14:11 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-cxf3-9h37-7rr8) ## Sources - [GitHub Advisory Database: GHSA-cxf3-9h37-7rr8](https://github.com/advisories/GHSA-cxf3-9h37-7rr8) - [OSV: GHSA-cxf3-9h37-7rr8](https://osv.dev/vulnerability/GHSA-cxf3-9h37-7rr8) - - - - - - Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code. ## Check whether this affects you A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet. - With the agentprime MCP server (), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: - In a browser: reads your lockfile in the browser, never uploading it. - Whether it touches your code, with file and line: the Claude Code plugin, - As JSON: , or `POST https://api.agentprime.io/v1/match` with your packages () --- The web page: . Everything for agents: .