Summary
rootless: /sys/fs/cgroup is writable when cgroupns isn't unshared in runc
Workarounds
- Condition 1: Unshare the cgroup namespace (
(docker|podman|nerdctl) run --cgroupns=private). This is the default behavior of Docker/Podman/nerdctl on cgroup v2 hosts. - Condition 2 (very rare): add
/sys/fs/cgrouptomaskedPaths
Impact
It was found that rootless runc makes /sys/fs/cgroup writable in following conditons:
- when runc is executed inside the user namespace, and the
config.jsondoes not specify the cgroup namespace to be unshared (e.g..,(docker|podman|nerdctl) run --cgroupns=host, with Rootless Docker/Podman/nerdctl) - or, when runc is executed outside the user namespace, and
/sysis mounted withrbind, ro(e.g.,runc spec --rootless; this condition is very rare)
A container may gain the write access to user-owned cgroup hierarchy /sys/fs/cgroup/user.slice/... on the host .
Other users's cgroup hierarchies are not affected.
CVE-2023-25809 has a CVSS score of 2.5 (Low). The vector is requires local access, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.1.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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v1.1.5 (planned)
Frequently Asked Questions
- What is CVE-2023-25809? CVE-2023-25809 is a low-severity security vulnerability in github.com/opencontainers/runc (go), affecting versions < 1.1.5. It is fixed in 1.1.5.
- How severe is CVE-2023-25809? CVE-2023-25809 has a CVSS score of 2.5 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/opencontainers/runc are affected by CVE-2023-25809? github.com/opencontainers/runc (go) versions < 1.1.5 is affected.
- Is there a fix for CVE-2023-25809? Yes. CVE-2023-25809 is fixed in 1.1.5. Upgrade to this version or later.
- Is CVE-2023-25809 exploitable, and should I be worried? Whether CVE-2023-25809 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-25809 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-25809? Upgrade
github.com/opencontainers/runcto 1.1.5 or later.