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Critical, CVSS 9.9amended

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

CVE-2026-61682GHSA-c8w2-fgvx-vhv4

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/kcp-dev/kcp 0.32.2, 0.31.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.9 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
EPSS
  • CVE-2026-61682: 0.38% estimated exploitation activity in the next 30 days; percentile 32.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-c8w2-fgvx-vhv4

  2. Revision 2 · amended ·

    Amended from osv record GO-2026-6517

  3. Revision 1 · created ·

    Published from osv record GHSA-c8w2-fgvx-vhv4

Agent brief

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# Patch Next advisory brief: CVE-2026-61682

Advisory: 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
IDs: CVE-2026-61682, GHSA-c8w2-fgvx-vhv4
Record: https://patchnext.com/advisories/cve-2026-61682 (revision 3, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/kcp-dev/kcp 0.32.2, 0.31.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/kcp-dev/kcp: affected < 0.31.4; >= 0.32.0, < 0.32.2; fixed in 0.32.2, 0.31.4

## Suggested inspection (read-only)
- Go github.com/kcp-dev/kcp: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/kcp-dev/kcp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-c8w2-fgvx-vhv4 (OSV record GHSA-c8w2-fgvx-vhv4 lists affected ranges: Go github.com/kcp-dev/kcp >=0 =0.32.0 <0.32.2 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6517 (OSV record GO-2026-6517 lists affected ranges: Go github.com/kcp-dev/kcp >=0 =0.32.0 <0.32.2 (fixed))
- Verified: https://github.com/advisories/GHSA-c8w2-fgvx-vhv4 (GitHub-reviewed advisory GHSA-c8w2-fgvx-vhv4 lists affected ranges: Go github.com/kcp-dev/kcp >=0 =0.32.0 <0.32.2)

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