# CVE-2021-25741: Symlink Exchange Can Allow Host Filesystem Access > Attackers can exploit symlink exchanges in subpath volume mounts to access or modify files on the host filesystem outside the intended volume. - **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`) - **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:** 16 Sep 2024 - **Also known as:** CLEANSTART-2025-RU72317, DEBIAN-CVE-2021-25741, GHSA-f5f7-6478-qm6p, GO-2022-0910, RHSA-2021:3631, RHSA-2021:3635, RHSA-2021:3642, RHSA-2021:3646 ## 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. Weakness: CWE-552 (Files or Directories Accessible to External Parties), CWE-20 (Improper Input Validation) ## 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 | Ecosystem | 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 | | `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 | | `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: 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. ## 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: - Exploit for CVE-2021-25741 vulnerability (github_poc): https://github.com/Betep0k/CVE-2021-25741 - fork on Betep0k/CVE-2021-25741/fork whose images is useless and test on metarget (github_poc): https://github.com/cdxiaodong/CVE-2021-25741 - CVE-2021-25741 POC in Zig (github_poc): https://github.com/Glutenfree69/ZigRaceExploit ## 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-2021-25741 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) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-25741 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-25741 - OSV: https://osv.dev/vulnerability/CVE-2021-25741 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-25741/ Summaries are generated and may contain mistakes; the official description above is the record.