CVE-2025-31133: runc container escape via "masked path" abuse due to mount race conditions

Description

runc is a CLI tool for spawning and running containers according to the OCI specification. In versions 1.2.7 and below, 1.3.0-rc.1 through 1.3.1, 1.4.0-rc.1 and 1.4.0-rc.2 files, runc would not perform sufficient verification that the source of the bind-mount (i.e., the container's /dev/null) was actually a real /dev/null inode when using the container's /dev/null to mask. This exposes two methods of attack: an arbitrary mount gadget, leading to host information disclosure, host denial of service, container escape, or a bypassing of maskedPaths. This issue is fixed in versions 1.2.8, 1.3.3 and 1.4.0-rc.3.

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack vector

Local

Complexity

High

Privileges

Low

User interaction

None

Confidentiality

High

Integrity

High

Availability

High

Scope

Changed

Exploitation

Is it being used?

Exploit prediction (EPSS)1.2% · higher than 69% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

RU

runc · opencontainers

< 1.2.8; >= 1.3.0-rc.1, < 1.3.3; >= 1.4.0-rc.1, <= 1.4.0-rc.3 · source: vendor, NVD