kcp's cache server is accessible without authentication or authorization checks

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-39429: 0.44% estimated exploitation activity in the next 30 days; percentile 37.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The cache server is directly exposed by the root shard and has no authentication or authorization in place. This allows anyone who can access the root shard to read and write to the cache server. Details The cache server is routed in the pre-mux chain in the shard code. The preHandlerChainMux is handled before any authn/authz in the cache server: https://github.com/kcp-dev/kcp/blob/aaf93d59cbcd0cefb70d94bd8959ce390547c4a2/pkg/server/config.go#L514-L518 This results in the cache server being proxied before any authn/authz in the handler chain takes place. Attack Vectors 1. Unauthenticated Read Access (Primary) An attacker can read all replicated resources from the cache without any credentials. This exposes: | Category | Resources | Severity | Reason | |---|---|---|---| | RBAC | clusterroles, clusterrolebindings (filtered by annotation) | High | Only subset with internal.kcp.io/replicate annotation: access rules, APIExport bind/content rules, WorkspaceType use rules. Reveals…

Published by the source

8 Apr 2026, 15:04 UTC

Last modified by the source

9 Apr 2026, 14:28 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3j3q-wp9x-585p

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# Patch Next advisory brief: CVE-2026-39429

Advisory: kcp's cache server is accessible without authentication or authorization checks
IDs: CVE-2026-39429, GHSA-3j3q-wp9x-585p
Record: https://patchnext.com/advisories/cve-2026-39429 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
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 0.30.3, 0.29.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/kcp-dev/kcp: affected >= 0.30.0, < 0.30.3; < 0.29.3; fixed in 0.30.3, 0.29.3

## 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://github.com/advisories/GHSA-3j3q-wp9x-585p (GitHub-reviewed advisory GHSA-3j3q-wp9x-585p lists affected ranges: Go github.com/kcp-dev/kcp >=0.30.0 =0 <0.29.3)

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