CVE-2023-25809 rootless: `/sys/fs/cgroup` is writable when cgroupns isn't unshared in runc
Rootless runc allows containers to write to host cgroup hierarchies when cgroup namespaces are not unshared, enabling privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-25809?
CVE-2023-25809 is a medium-severity vulnerability in opencontainers runc, published on 29 Mar 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
runc is a CLI tool for spawning and running containers according to the OCI specification. In affected versions it was found that rootless runc makes `/sys/fs/cgroup` writable in following conditons: 1. when runc is executed inside the user namespace, and the `config.json` does not specify the cgroup namespace to be unshared (e.g.., `(docker|podman|nerdctl) run --cgroupns=host`, with Rootless Docker/Podman/nerdctl) or 2. when runc is executed outside the user namespace, and `/sys` is mounted with `rbind, 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. Users are advised to upgrade to version 1.1.5. Users unable to upgrade may unshare the cgroup namespace (`(docker|podman|nerdctl) run --cgroupns=private)`. This is the default behavior of Docker/Podman/nerdctl on cgroup v2 hosts. or add `/sys/fs/cgroup` to `maskedPaths`.
Weakness: CWE-281
Which versions are affected by CVE-2023-25809?
3 open source packages ship an affected version, including github.com/opencontainers/runc. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/opencontainers/runc Go | All versions | 1.1.5 |
github.com/opencontainers/runc Go | All versions | 1.1.5 |
github.com/opencontainers/runc Go | All versions | 1.1.5 |
Products include Linuxfoundation Runc.
How do I fix CVE-2023-25809?
Upgrade github.com/opencontainers/runc to 1.1.5 or later.
Is CVE-2023-25809 being exploited?
There is no known exploitation of CVE-2023-25809 in the wild and no public exploit code.
Other vulnerabilities in opencontainers runc
- CVE-2025-52565 container escape due to /dev/console mount and related races
- CVE-2025-31133 runc container escape via "masked path" abuse due to mount race conditions
- CVE-2025-52881 runc: LSM labels can be bypassed with malicious config using dummy procfs files
- CVE-2023-28642 AppArmor bypass with symlinked /proc in runc
- CVE-2024-45310 runc can be confused to create empty files/directories on the host
Sources
Also known as AZL-25851, CLEANSTART-2026-OE93355, DEBIAN-CVE-2023-25809, GHSA-m8cg-xc2p-r3fc, GO-2023-1682, UBUNTU-CVE-2023-25809.