Executive brief
kcp is a control plane used to manage workloads across different environments. A security flaw allows unauthenticated users to access the system's internal cache server, which is responsible for storing critical configuration and infrastructure data. An attacker could read sensitive information about the network topology and security rules, or potentially exploit a timing window to temporarily gain higher privileges, leading to unauthorized data access or disruption of security policies.
Technical details
The kcp cache server is routed within the pre-mux chain of the shard code (preHandlerChainMux), which executes before any authentication or authorization handlers. This architectural flaw allows unauthenticated network-reachable attackers to perform CRUD operations on the cache server. Impact includes full read access to replicated resources such as RBAC cluster roles, API exports, and infrastructure topology. While a replication controller acts as a self-healing mechanism by deleting unauthorized write attempts, a race condition exists where injected RBAC rules could be briefly evaluated by the GlobalAuthorizer before deletion, potentially allowing temporary privilege escalation. The vulnerability is fixed in versions 0.29.3 and 0.30.3.
Affected products
- kcp-dev kcp < 0.29.3, >= 0.30.0, < 0.30.3
Timeline
- 2026-04-02: patched: Versions 0.29.3 and 0.30.3 released
- 2026-04-07: advisory: GitHub Security Advisory GHSA-3j3q-wp9x-585p published
- 2026-04-08: disclosed: CVE-2026-39429 published