# CVE-2026-39429: kcp's cache server is accessible without authentication or authorization checks

> Attackers can read and write to the cache server without authentication because the root shard exposes it without checks.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** GHSA-3j3q-wp9x-585p, GO-2026-5088

## What is CVE-2026-39429?

CVE-2026-39429 is a high-severity missing authorization vulnerability in kcp-dev kcp, published on 8 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

kcp is a Kubernetes-like control plane for form-factors and use-cases beyond Kubernetes and container workloads. Prior to 0.30.3 and 0.29.3, 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. This vulnerability is fixed in 0.30.3 and 0.29.3.

Weakness: CWE-862 (Missing Authorization), CWE-302 (Authentication Bypass by Assumed-Immutable Data)

## Which versions are affected by CVE-2026-39429?

5 open source packages ship an affected version, including github.com/kcp-dev/kcp. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/kcp-dev/kcp` | Go | All versions | 0.29.3, 0.30.3 |
| `github.com/kcp-dev/kcp` | Go | All versions | 0.29.3 |
| `github.com/kcp-dev/kcp` | Go | All versions | 0.29.3 |
| `github.com/kcp-dev/kcp` | Go | From 0.30.0 | 0.30.3 |
| `github.com/kcp-dev/kcp` | Go | From 0.30.0 | 0.30.3 |

Products: Kcp Kcp.

## How do I fix CVE-2026-39429?

Upgrade github.com/kcp-dev/kcp to a fixed version for your release line: 0.29.3 or 0.30.3.

## Is CVE-2026-39429 being exploited?

There is no known exploitation of CVE-2026-39429 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-39429 and fix it if it is affected.

What it is: CVE-2026-39429 is a high-severity missing authorization vulnerability in kcp-dev kcp, published on 8 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-39429 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/kcp-dev/kcp (Go): affected all versions; fixed in 0.29.3, 0.30.3
- github.com/kcp-dev/kcp (Go): affected all versions; fixed in 0.29.3
- github.com/kcp-dev/kcp (Go): affected all versions; fixed in 0.29.3
- github.com/kcp-dev/kcp (Go): affected from 0.30.0; fixed in 0.30.3
- github.com/kcp-dev/kcp (Go): affected from 0.30.0; fixed in 0.30.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-39429/ (Markdown: https://insights.sbomify.com/CVE-2026-39429/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39429
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39429
- OSV: https://osv.dev/vulnerability/CVE-2026-39429

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-39429/
Summaries are generated and may contain mistakes; the official description above is the record.