labstack
Echo: Rejected WebSocket upgrades can bypass Echo route-level access controls
Not on CISA's list of exploited flaws, and not in the news we track.
CVE-2026-118264Critical9.1
Black Shard's team can check your exposure to CVE-2026-118264 and take the fix off your plate.
Echo is a Go web framework. From 4.0.0 until 4.16.1 and 5.4.1, Echo's Proxy middleware selects a raw tunnel from a client WebSocket upgrade request before verifying that the configured upstream accepted the upgrade. If the upstream rejects the upgrade with an ordinary keep-alive response, later HTTP requests on the connection are sent directly to that upstream without passing through Echo's router or route-specific middleware. This can bypass authentication or authorization enforced only by Echo routes, but requires an accessible proxy route, a cooperating rejected-upgrade response, and a target without independent upstream authorization. This issue is fixed in 4.16.1 and 5.4.1.
Black Shard's team can check your exposure, take a fix off your plate or step in on a live incident.
Chance of exploitation in the next 30 days
0.43%
EPSS score from FIRST
Updated 13 Nov 2026, 12:03 UTC, 31 of 36 sources answering.
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