CVE-2025-31133
Description
A flaw was found in runc. This flaw exploits an issue with how masked paths are implementedin runc. When masking files, runc will bind-mount the container's /dev/null inode on top of the file. However, if an attacker can replace /dev/null with a symlink to some other procfs file, runc will instead bind-mount the symlink target read-write.
Statement
Red Hat considers this as an Important flaw since the impact is limited to local attack with minimal privileges in order to jeopardize the environment.
Mitigation
Potential mitigations for this issue include:
* Using user namespaces, with the host root user not mapped into the container's namespace. procfs file permissions are managed using Unix
DAC and thus user namespaces stop a container process from being able to write to them.
* Not running as a root user in the container (this includes disabling setuid binaries with noNewPrivileges). As above, procfs file permissions are managed using Unix DAC and thus non-root users cannot write to them.
* Depending on the maskedPath configuration (the default configuratio nonly masks paths in /proc and /sys), using an AppArmor that blocks unexpectedwrites to any maskedPaths (as is the case with the defaultprofile used by Docker and Podman) will block attempts to exploit this issue. However, CVE-2025-52881 allows an attacker to bypass LSMlabels, and so this mitigation is not helpful when considered incombination with CVE-2025-52881.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.2 | 7.8 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | High | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | Required | None | N/A |
| Scope | Changed | Changed | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality,Integrity,Access Control
Technical Impact: Read Files or Directories; Modify Files or Directories; Bypass Protection Mechanism
An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism then an attacker may be able to bypass the mechanism.
Other
Technical Impact: Execute Unauthorized Code or Commands
Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.
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