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

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kcp is a Kubernetes-like control plane for form-factors and use-cases beyond Kubernetes and container workloads. Prior to 0.31.4 and 0.32.2, the kcp front-proxy does not remove inbound X-Remote-User, X-Remote-Group, or X-Remote-Extra-* identity headers before forwarding requests to shards. Any authenticated tenant can inject X-Remote-Group: system:masters, authorization.kcp.io/warrant, authentication.kcp.io/scopes, or a group used for per-workspace required-group gating, and the shard trusts these values as authenticated identity assertions. This allows cross-workspace impersonation, authorization bypass, and arbitrary reading, writing, or deletion of resources, secrets, RBAC data, APIExports, APIBindings, and LogicalClusters. This issue is fixed in versions 0.31.4 and 0.32.2.

Source published

18 Sep 2026 16:11:46 UTC

Source modified

21 Sep 2026 20:50:17 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

kcp is a Kubernetes-like control plane for form-factors and use-cases beyond Kubernetes and container workloads. Prior to 0.31.4 and 0.32.2, the kcp front-proxy does not remove inbound X-Remote-User, X-Remote-Group, or X-Remote-Extra-* identity headers before forwarding requests to shards. Any authenticated tenant can inject X-Remote-Group: system:masters, authorization.kcp.io/warrant, authentication.kcp.io/scopes, or a group used for per-workspace required-group gating, and the shard trusts these values as authenticated identity assertions. This allows cross-workspace impersonation, authorization bypass, and arbitrary reading, writing, or deletion of resources, secrets, RBAC data, APIExports, APIBindings, and LogicalClusters. This issue is fixed in versions 0.31.4 and 0.32.2.

Source published

Sep 18, 2026, 4:11:46 PM (timezone not stated)

Source modified

Sep 21, 2026, 8:50:17 PM (timezone not stated)

Observed here

11 Nov 2026 15:02:57 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

kcp is a Kubernetes-like control plane for form-factors and use-cases beyond Kubernetes and container workloads. Prior to 0.31.4 and 0.32.2, the kcp front-proxy does not remove inbound X-Remote-User, X-Remote-Group, or X-Remote-Extra-* identity headers before forwarding requests to shards. Any authenticated tenant can inject X-Remote-Group: system:masters, authorization.kcp.io/warrant, authentication.kcp.io/scopes, or a group used for per-workspace required-group gating, and the shard trusts these values as authenticated identity assertions. This allows cross-workspace impersonation, authorization bypass, and arbitrary reading, writing, or deletion of resources, secrets, RBAC data, APIExports, APIBindings, and LogicalClusters. This issue is fixed in versions 0.31.4 and 0.32.2.

Source published

18 Sep 2026 16:17:07 UTC

Source modified

24 Sep 2026 21:25:27 UTC

Observed here

25 Oct 2026 14:19:22 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

# Summary The 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. ## Impact In 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. Because 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: - assert `X-Remote-Group: system:masters` and act as cluster super-user, bypassing the entire kcp authorizer chain in every workspace on the shard; - forge `authorization.kcp.io/warrant` to assume an arbitrary user/group identity via kcp's delegated-identity mechanism; - forge `authentication.kcp.io/scopes` to escape the cluster-scoping that confines service-account and impersonated identities to their origin workspace; - satisfy per-workspace required-group gating by injecting the required group. The 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. # Patches Fixed 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. Operators should upgrade to a patched release. No configuration changes are required after upgrading. # Workarounds There 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. Credit to [5ud0er](https://github.com/5ud0er) / Tarmo Technologies.

Source published

18 Sep 2026 17:15:49 UTC

Source modified

28 Sep 2026 17:11:09 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Publisher rating · CRITICAL

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 in github.com/kcp-dev/kcp

Source published

28 Sep 2026 16:43:40 UTC

Source modified

28 Sep 2026 17:00:16 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.