# CVE-2021-25740: Holes in EndpointSlice Validation Enable Host Network Hijack

> Attackers can hijack host network traffic via confused deputy attacks in EndpointSlice validation, bypassing network restrictions.

- **Severity:** Low 3.1 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Sep 2021
- **Updated:** 1 Jun 2026
- **Also known as:** AZL-89312, DEBIAN-CVE-2021-25740, GHSA-vw47-mr44-3jf9, MINI-2hj8-5mrc-xh8c, MINI-2v84-775m-2c3g, MINI-3256-rwg7-g8xr, MINI-4p86-6c66-43q2, MINI-6g58-rxpp-4g8h, MINI-8mr7-prqp-7fmv, MINI-cx94-p8gq-hj6h, MINI-gfj7-c6gh-425c, MINI-h67m-926v-rhc6, MINI-m4qc-pc8f-gf27, MINI-m594-9cx4-3f3v, MINI-pm5g-pqrw-7hq9, OESA-2022-2139

## What is CVE-2021-25740?

CVE-2021-25740 is a low-severity server-side request forgery vulnerability in Kubernetes Kubernetes, published on 20 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A security issue was discovered with Kubernetes that could enable users to send network traffic to locations they would otherwise not have access to via a confused deputy attack.

Weakness: CWE-610 (Externally Controlled Reference to a Resource in Another Sphere), CWE-441 (Unintended Proxy or Intermediary)

## Which versions are affected by CVE-2021-25740?

2 open source packages ship an affected version, including k8s.io/kubernetes. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `k8s.io/kubernetes` | Go | All versions to 1.22.2 | None |
| `k8s.io/kubernetes` | Go | All versions to 1.22.2 | None |

Products: Kubernetes Kubernetes.

## How do I fix CVE-2021-25740?

Apply the vendor's patch.

## Is CVE-2021-25740 being exploited?

There is no known exploitation of CVE-2021-25740 in the wild and no public exploit code.

## Other vulnerabilities in Kubernetes Kubernetes

- [CVE-2018-1002105](https://insights.sbomify.com/CVE-2018-1002105/): Privilege Escalation in Kubernetes (critical 9.8)
- [CVE-2017-1000056](https://insights.sbomify.com/CVE-2017-1000056/): Kubernetes Privilege Escalation (critical 9.8)
- [CVE-2016-1906](https://insights.sbomify.com/CVE-2016-1906/): Authorization bypass in Openshift (critical 9.8)
- [CVE-2023-3676](https://insights.sbomify.com/CVE-2023-3676/): Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation (high 8.8)
- [CVE-2023-3955](https://insights.sbomify.com/CVE-2023-3955/): Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-25740 and fix it if it is affected.

What it is: CVE-2021-25740 is a low-severity server-side request forgery vulnerability in Kubernetes Kubernetes, published on 20 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-25740 in the wild and no public exploit code.

Affected packages and fixed versions:
- k8s.io/kubernetes (Go): affected all versions up to 1.22.2; no fix listed
- k8s.io/kubernetes (Go): affected all versions up to 1.22.2; no fix listed

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-2021-25740/ (Markdown: https://insights.sbomify.com/CVE-2021-25740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-25740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-25740
- OSV: https://osv.dev/vulnerability/CVE-2021-25740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-25740/
Summaries are generated and may contain mistakes; the official description above is the record.