CVE-2021-25741 Symlink Exchange Can Allow Host Filesystem Access
High 8.8
Published
Updated
Check this codebase for CVE-2021-25741 and fix it if it is affected.
What it is: CVE-2021-25741 is a high-severity path traversal 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-2021-25741 in the wild and no public exploit code.
Affected packages and fixed versions:
- k8s.io/kubernetes (Go): affected all versions; fixed in 1.19.15, 1.20.11, 1.21.5, 1.22.2
- k8s.io/kubernetes (Go): affected all versions; fixed in 1.19.15
- k8s.io/kubernetes (Go): affected all versions; fixed in 1.19.15
- k8s.io/kubernetes (Go): affected from 1.20.0; fixed in 1.20.11
- k8s.io/kubernetes (Go): affected from 1.20.0; fixed in 1.20.11
- k8s.io/kubernetes (Go): affected from 1.21.0; fixed in 1.21.5
- k8s.io/kubernetes (Go): affected from 1.21.0; fixed in 1.21.5
- k8s.io/kubernetes (Go): affected from 1.22.0; fixed in 1.22.2
- k8s.io/kubernetes (Go): affected from 1.22.0; fixed in 1.22.2
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-2021-25741/ (Markdown: https://insights.sbomify.com/CVE-2021-25741/index.md)
Attackers can exploit symlink exchanges in subpath volume mounts to access or modify files on the host filesystem outside the intended volume.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-25741?
CVE-2021-25741 is a high-severity path traversal 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 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.
Which versions are affected by CVE-2021-25741?
9 open source packages ship an affected version, including k8s.io/kubernetes. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
k8s.io/kubernetes Go | All versions | 1.19.15, 1.20.11, 1.21.5, 1.22.2 |
k8s.io/kubernetes Go | All versions | 1.19.15 |
k8s.io/kubernetes Go | All versions | 1.19.15 |
k8s.io/kubernetes Go | From 1.20.0 | 1.20.11 |
k8s.io/kubernetes Go | From 1.20.0 | 1.20.11 |
k8s.io/kubernetes Go | From 1.21.0 | 1.21.5 |
3 more packages
k8s.io/kubernetes Go | From 1.21.0 | 1.21.5 |
k8s.io/kubernetes Go | From 1.22.0 | 1.22.2 |
k8s.io/kubernetes Go | From 1.22.0 | 1.22.2 |
Linux distribution packages (25)
atomic-openshift Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-clients Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-clients-redistributable Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-docker-excluder Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-excluder Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-hyperkube Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-hypershift Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-master Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-node Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-pod Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-sdn-ovs Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-template-service-broker Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
atomic-openshift-tests Red Hat:openshift:3.11::el7 | All versions | 0:3.11.524-1.git.0.2dffce7.el7 |
openshift Red Hat:openshift:4.6::el7 | All versions | 0:4.6.0-202109180038.p0.git.d5ed12c.assembly.stream.el7 |
openshift-hyperkube Red Hat:openshift:4.6::el7 | All versions | 0:4.6.0-202109180038.p0.git.d5ed12c.assembly.stream.el7 |
openshift Red Hat:openshift:4.6::el8 | All versions | 0:4.6.0-202109180038.p0.git.d5ed12c.assembly.stream.el8 |
openshift-hyperkube Red Hat:openshift:4.6::el8 | All versions | 0:4.6.0-202109180038.p0.git.d5ed12c.assembly.stream.el8 |
openshift Red Hat:openshift:4.7::el7 | All versions | 0:4.7.0-202109172126.p0.git.bbbc079.assembly.stream.el7 |
openshift-hyperkube Red Hat:openshift:4.7::el7 | All versions | 0:4.7.0-202109172126.p0.git.bbbc079.assembly.stream.el7 |
openshift Red Hat:openshift:4.7::el8 | All versions | 0:4.7.0-202109172126.p0.git.bbbc079.assembly.stream.el8 |
openshift-hyperkube Red Hat:openshift:4.7::el8 | All versions | 0:4.7.0-202109172126.p0.git.bbbc079.assembly.stream.el8 |
openshift Red Hat:openshift:4.8::el7 | All versions | 0:4.8.0-202109180335.p0.git.a620f50.assembly.stream.el7 |
openshift-hyperkube Red Hat:openshift:4.8::el7 | All versions | 0:4.8.0-202109180335.p0.git.a620f50.assembly.stream.el7 |
openshift Red Hat:openshift:4.8::el8 | All versions | 0:4.8.0-202109180335.p0.git.a620f50.assembly.stream.el8 |
openshift-hyperkube Red Hat:openshift:4.8::el8 | All versions | 0:4.8.0-202109180335.p0.git.a620f50.assembly.stream.el8 |
Products include Kubernetes Kubernetes.
How do I fix CVE-2021-25741?
Upgrade k8s.io/kubernetes to a fixed version for your release line: 1.19.15, 1.20.11, 1.21.5 or 1.22.2.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2021-25741 being exploited?
There is no known exploitation of CVE-2021-25741 in the wild and no public exploit code.
Public exploit code: 3 proofs of concept on GitHub.
Other vulnerabilities in Kubernetes Kubernetes
- CVE-2018-1002105 Privilege Escalation in Kubernetes
- CVE-2017-1000056 Kubernetes Privilege Escalation
- CVE-2016-1906 Authorization bypass in Openshift
- CVE-2023-3676 Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation
- CVE-2023-3955 Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation
Sources
Also known as CLEANSTART-2025-RU72317, DEBIAN-CVE-2021-25741, GHSA-f5f7-6478-qm6p, GO-2022-0910, RHSA-2021:3631, RHSA-2021:3635 and 2 more.