kcp Front-Proxy Lets Attackers Impersonate Any User

kcp, the Kubernetes-like control plane for multi-tenant and cloud-native workloads, patched a critical authentication bypass on September 18, 2026. CVE-2026-61682 carries a CVSS score of 9.9.

The flaw is in the kcp front-proxy. Kubernetes and Kubernetes-like systems use X-Remote-User and related headers to pass user identity between proxy layers. The kcp front-proxy did not strip those headers from inbound requests before passing them to the backend. Anyone who could reach the front-proxy directly could set X-Remote-User to any value and be treated as that identity by the control plane, including cluster administrators.

No authentication required. No credentials to steal. Just reach the endpoint and name yourself.

Affected versions: kcp prior to 0.31.4 (on the 0.31.x branch) and prior to 0.32.2 (on the 0.32.x branch). Source: NVD.

What to do

Upgrade to kcp 0.31.4 or 0.32.2. No workaround is documented. The fix strips impersonation headers from inbound requests at the front-proxy layer before forwarding them.

If you can’t patch immediately, restrict access to the kcp front-proxy to trusted internal networks. The vulnerability requires direct network access to the proxy endpoint, so a network boundary buys time.

After upgrading, audit recent access logs for unexpected use of impersonation headers. Any request that arrived with a non-empty X-Remote-User from outside your control plane’s trusted internal sources should be investigated.

kcp runs in multi-tenant environments where namespace isolation is the primary security boundary. An impersonation bypass at the control plane level collapses that boundary entirely for the duration of exposure.

Related: Orkes Conductor critical RCE CVE-2026-58138 actively exploited and Cisco ISE CVSS 10.0 auth bypass CVE-2026-76460.