SingularityCE and SingularityPRO are open source container platforms. Prior to SingularityCE 4.3.5 and SingularityPRO 4.1.11 and 4.3.5, 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. The attacker must cause the user to run a malicious container image that redirects the mount of /proc to 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. The attacker must also control 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. This vulnerability is fixed in SingularityCE 4.3.5 and SingularityPRO 4.1.11 and 4.3.5.

Affected: Go: github.com/sylabs/singularity/v4

### 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 `/proc` to 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](https://github.com/opencontainers/runc/security/advisories/GHSA-cgrx-mc8f-2prm) are not relevant. Processes running in non-root containers are subject t…

Affected: Ubuntu:Pro:18.04:LTS: singularity-container, Ubuntu:Pro:24.04:LTS: singularity-container, Ubuntu:25.10: singularity-container, Ubuntu:26.04:LTS: singularity-container

SingularityCE and SingularityPRO are open source container platforms. Prior to SingularityCE 4.3.5 and SingularityPRO 4.1.11 and 4.3.5, 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. The attacker must cause the user to run a malicious container image that redirects the mount of /proc to 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. The attacker must also control 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. This vulnerability is fixed in SingularityCE 4.3.5 and SingularityPRO 4.1.11 and 4.3.5.