{"id":"GHSA-c8w2-fgvx-vhv4","revision":"90b0a42f3fcb44e5bdc7f1ecfd9c2d0c","records":[{"revision":"90b0a42f3fcb44e5bdc7f1ecfd9c2d0c","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-c8w2-fgvx-vhv4","aliases":["CVE-2026-61682","GO-2026-6517"],"title":"kcp front-proxy does not strip inbound X-Remote-* identity headers, allowing any authenticated client to inject groups/warrants and impersonate system:masters in any workspace","description":"# Summary\n\nThe kcp front-proxy fails to strip client-supplied identity headers before forwarding requests to shards. Any authenticated tenant can inject their own `X-Remote-Group` and `X-Remote-Extra-*` headers, which the shard trusts as a verified identity assertion — allowing a low-privilege user to escalate to cluster administrator (`system:masters`) and read, write, or delete resources in any workspace on the shard. This is a complete multi-tenant isolation and authorization bypass.\n\n## Impact \n\nIn a sharded kcp deployment, external clients reach shards through the front-proxy, which authenticates the client and then forwards the resulting identity to the shard using Kubernetes request-header authentication (`X-Remote-User` / `X-Remote-Group` / `X-Remote-Extra-*`). The shard trusts these headers because they arrive over the front-proxy's mutually-authenticated connection.\n\nBecause the front-proxy appended its identity headers instead of replacing them — and never removed any copies the client sent — an authenticated attacker could smuggle forged identity headers through to the shard. With this, an attacker holding any ordinary credential (client certificate, OIDC token, or service-account token) and no special privileges could:\n\n- assert `X-Remote-Group: system:masters` and act as cluster super-user, bypassing the entire kcp authorizer chain in every workspace on the shard;\n- forge `authorization.kcp.io/warrant` to assume an arbitrary user/group identity via kcp's delegated-identity mechanism;\n- forge `authentication.kcp.io/scopes` to escape the cluster-scoping that confines service-account and impersonated identities to their origin workspace;\n- satisfy per-workspace required-group gating by injecting the required group.\n\nThe result is arbitrary read/write/delete access to any tenant's resources, secrets, RBAC, APIExports/APIBindings, and LogicalClusters — a cross-workspace access break and authorizer bypass across the proxy's trust boundary.\n\n\n# Patches\nFixed in v0.31.4, 0.32.2. The front-proxy and the shard's in-process local-proxy now unconditionally remove any inbound `X-Remote-*` identity headers before stamping the authenticated identity, so no client-supplied value can be forwarded to a shard.\n\nOperators should upgrade to a patched release. No configuration changes are required after upgrading.\n\n# Workarounds\n\nThere is no complete workaround other than upgrading. Deployments that terminate client connections at an external proxy capable of stripping `X-Remote-User`, `X-Remote-Group`, and all `X-Remote-Extra-*` headers from inbound requests before they reach the kcp front-proxy can mitigate exposure in the interim.\n\nCredit to [5ud0er](https://github.com/5ud0er) / Tarmo Technologies.","state":0,"publishedAt":"2026-09-18T17:15:49+00:00","modifiedAt":"2026-09-28T17:11:09.1413568+00:00","affected":[{"ecosystem":"Go","name":"github.com/kcp-dev/kcp","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"0.31.4"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"Go","name":"github.com/kcp-dev/kcp","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.32.0"},{"kind":"fixed","version":"0.32.2"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"CRITICAL"}],"references":["https://github.com/kcp-dev/kcp/security/advisories/GHSA-c8w2-fgvx-vhv4","https://github.com/kcp-dev/kcp/commit/7437cdcfec8f927d1a9bf1b2dd1e075d038e27ca","https://github.com/kcp-dev/kcp","https://github.com/kcp-dev/kcp/releases/tag/v0.31.4","https://github.com/kcp-dev/kcp/releases/tag/v0.32.2"],"sourceUrl":"https://github.com/advisories/GHSA-c8w2-fgvx-vhv4","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-c8w2-fgvx-vhv4","identifiers":["GHSA-c8w2-fgvx-vhv4","CVE-2026-61682","GO-2026-6517"]},"retained":false,"historicalAffected":[]}],"coverage":[]}