GHSA-wwrx-w7c9-rf87
MEDIUMSingluarity ineffectively applies selinux / apparmor LSM process labels
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/sylabs/singularity/v4🐹github.com/sylabs/singularity/v4Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Native Mode (default)
Singularity's default native runtime allows users to apply restrictions to container processes using the apparmor or selinux Linux Security Modules (LSMs), via the --security selinux:<label> or --security apparmor:<profile> flags.
LSM labels are written to process or thread attrs/exec under /proc. If a user relies on LSM restrictions to prevent malicious operations then, under certain circumstances, an attacker can redirect the LSM label write operation so that it is ineffective. This requires:
- The attacker to cause the user to run a malicious container image that redirects the mount of
/procto the destination of a shared mount, either known to be configured on the target system, or that will be specified by the user when running the container. - Control of the content of the shared mount, for example through another malicious container which also binds it, or as a user with relevant permissions on the host system it is bound from.
Note that Singularity does not attempt to prevent damaging operations, or container escape, from containers that are started as the host root user. When a non-root user starts a container any LSM writes to /proc are performed as that user. For these reasons, the denial-of-service and container escape attacks detailed in runc CVE-2025-52881 are not relevant. Processes running in non-root containers are subject to the standard permissions for the non-root account used, and cannot escalate privilege, even when intended container-specific LSM labels are not correctly applied.
In addition, a bug in the detection of selinux support in Singularity's default setuid flow means that --security selinux:<label> flags may not be applied, even in the absence of an attack - but in this case a warning message is emitted, indicating that selinux is unavailable. This warning may be may be overlooked, mis-interpreted, or not seen when singularity is run from a script or other tool. Failure to apply requested restrictions should result in a fatal error, rather than a warning message.
OCI-Mode
Singularity's OCI-mode is unaffected as it does not currently support applying LSM restrictions via the --security flag.
Patches
Ineffective write of selinux process labels is addressed via an update to the containers/selinux dependency in https://github.com/sylabs/singularity/pull/3850. This update brings in the upstream fix for CVE-2025-52881 in this dependency.
Ineffective write of apparmor process labels is addressed in commit 5af3e79.
Failure to detect apparmor / selinux support, when --security flags are provided, is made an error rather than a warning in commit 2788296.
Workarounds
There are no known workarounds, other than to define system-wide apparmor / selinux policy for Singularity itself. This would apply to all containers, not just those run with the --security flags. Additionally, restrictions that are reasonable to apply to container processes may impact the functionality of Singularity.
References
Related vulnerabilities in runc:
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/sylabs/singularity/v4 | ≥ 4.2.0-rc.1&&< 4.3.5 | 4.3.5 |
| 🐹Go | github.com/sylabs/singularity/v4 | all versions | 4.1.11 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sylabs/singularity/v4. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/sylabs/singularity/v4 to 4.3.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wwrx-w7c9-rf87 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-wwrx-w7c9-rf87 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-wwrx-w7c9-rf87. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-wwrx-w7c9-rf87 in your dependencies?
O3 detects GHSA-wwrx-w7c9-rf87 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.