Vulnerability Database

326,895

Total vulnerabilities in the database

devices resource list treated as a blacklist by default

Impact

Contrary to the OCI runtime specification, runc's implementation of the linux.resources.devices list was a black-list by default. This means that users who created their own config.json objects and didn't prefix a deny-all rule ({"allow": false, "permissions": "rwm"} or equivalent) were not provided protection by the devices cgroup. This would allow malicious containers (with sufficient privileges) to create arbitrary device inodes (assuming they have CAP_MKNOD) and operate on any device inodes they may have access to (assuming they have regular Unix DAC permissions).

However, most (if not all) programs that make use of runc include this deny-all rule. This was most likely added before the specification mandated a white-list of devices, and the fact that all programs wrote their own deny-all rule obscured the existence of this bug for several years. In fact, even the specification's examples include a default deny-all rule! We therefore believe that while this is a security bug (and has been fixed as such), it was almost certainly not exploitable in the wild due to the inclusion of default deny-all rules by all known users of runc -- hence why this advisory has low severity.

Patches

This issue has been fixed in a patch that was part of a larger rework of the devices cgroup code in runc -- which lead to the discovery of this security bug. Users should upgrade to 1.0.0-rc91 as soon as it is released, or wait for your distribution to backport the relevant fixes.

Workarounds

If you are using runc directly, ensure that there is a deny-all entry at the beginning of linux.resources.devices -- such an entry would look like {"allow": false, "permissions": "rwm"} (all other fields are ignored, though type must be set to "a" or null if it is present).

Users which consume runc through another program should check whether their containers are operating under a white-list -- this can be done by reading /sys/fs/cgroup/devices/devices.list inside the container. If the file contains only the entry a *:* rwm (meaning the cgroup is in black-list mode, which likely means "allow all device access") then your containers are vulnerable to this issue.

As always, we recommend in the strongest possible terms that all of our users enable user namespaces on all of their workloads (or pressure their vendors to do so). User namespaces are one of the most significant defense-in-depth protections you can enable for containers, and have prevented many container-related vulnerabilities (both kernel 0days as well as bugs in container runtimes, such as this one).

References

For more information

If you have any questions or comments about this advisory:

No technical information available.

No CWE or OWASP classifications available.

Software From Fixed in
Go icon github.com/opencontainers/runc - 1.0.0-rc91

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.