# Kube-proxy may unintentionally forward traffic

Advisory record · `GHSA-35c7-w35f-xwgh`

- **Identifiers:** `GHSA-35c7-w35f-xwgh` · `CVE-2021-25736` · `GO-2023-2159`
- **State:** Confirmed
- **Severity:** CVSS 5.8 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-114](https://cwe.mitre.org/data/definitions/114.html)
- **Tags:** [CWE-114](https://agentprime.io/advisories/tag/cwe-114.md)
- **Published:** 30 Oct 2023
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 30 Oct 2023, 03:30 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `k8s.io/kubernetes` (Go): affected `<1.21.0`; fixed in `1.21.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Kubernetes (k8s.io/kubernetes) versions before 1.21.0 are affected. On Windows, kube-proxy can forward traffic meant for a LoadBalancer Service to local processes listening on the same port when the LoadBalancer controller does not set the status.loadBalancer.ingress\[\].ip field. Upgrade to 1.21.0 or later. Clusters where the LoadBalancer controller sets that field are not affected.

Written 2 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.8 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N`, from CNA (kubernetes)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0092, the 60th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:15 UTC: First seen by agentprime
- 31 Oct 2026, 14:15 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-35c7-w35f-xwgh)

## Sources

- [GitHub Advisory Database: GHSA-35c7-w35f-xwgh](https://github.com/advisories/GHSA-35c7-w35f-xwgh)
- [OSV: GHSA-35c7-w35f-xwgh](https://osv.dev/vulnerability/GHSA-35c7-w35f-xwgh)
- <https://nvd.nist.gov/vuln/detail/CVE-2021-25736>
- <https://github.com/kubernetes/kubernetes/pull/99958>
- <https://github.com/kubernetes/kubernetes/commit/b014610de3e5cf1bb0f7844b5758d29fc18b75e6>
- <https://github.com/kubernetes/kubernetes>
- <https://groups.google.com/g/kubernetes-security-announce/c/lIoOPObO51Q/m/O15LOazPAgAJ>
- <https://security.netapp.com/advisory/ntap-20231221-0003>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-35c7-w35f-xwgh>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-35c7-w35f-xwgh/>. Everything for agents: <https://agentprime.io/llms.txt>.