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rootless: `/sys/fs/cgroup` is writable when cgroupns isn't unshared in runc

Low severity GitHub Reviewed Published Mar 29, 2023 in opencontainers/runc • Updated Mar 30, 2023

Package

gomod github.com/opencontainers/runc (Go)

Affected versions

< 1.1.5

Patched versions

1.1.5

Description

Impact

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)
  2. or, 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.

Patches

v1.1.5 (planned)

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/cgroup to maskedPaths

References

@cyphar cyphar published to opencontainers/runc Mar 29, 2023
Published by the National Vulnerability Database Mar 29, 2023
Published to the GitHub Advisory Database Mar 30, 2023
Reviewed Mar 30, 2023
Last updated Mar 30, 2023

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
High
Privileges required
High
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:N/I:N/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(9th percentile)

Weaknesses

Improper Preservation of Permissions

The product does not preserve permissions or incorrectly preserves permissions when copying, restoring, or sharing objects, which can cause them to have less restrictive permissions than intended. Learn more on MITRE.

CVE ID

CVE-2023-25809

GHSA ID

GHSA-m8cg-xc2p-r3fc

Source code

Credits

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