runc container escape via "masked path" abuse due to mount race conditions

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.3 · CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H · score source

EPSS

• CVE-2025-31133: 1.24% estimated exploitation activity in the next 30 days; percentile 69.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact

The OCI runtime specification has a maskedPaths feature that allows for files or directories to be "masked" by placing a mount on top of them to conceal their contents. This is primarily intended to protect against privileged users in non-user-namespaced from being able to write to files or access directories that would either provide sensitive information about the host to containers or allow containers to perform destructive or other privileged operations on the host (examples include /proc/kcore, /proc/timerlist, /proc/acpi, and /proc/keys). maskedPaths can be used to either mask a directory or a file -- directories are masked using a new read-only tmpfs instance that is mounted on top of the masked path, while files are masked by bind-mounting the container's /dev/null on top of the masked path. In all known versions of runc, when using the container's /dev/null to mask files, runc would not perform sufficient verification that the source of the bind-mount (i.e., the…

Published by the source

5 Nov 2025, 16:37 UTC

Last modified by the source

6 Nov 2025, 23:12 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9493-h29p-rfm2

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# Patch Next advisory brief: CVE-2025-31133

Advisory: runc container escape via "masked path" abuse due to mount race conditions
IDs: CVE-2025-31133, GHSA-9493-h29p-rfm2
Record: https://patchnext.com/advisories/cve-2025-31133 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/opencontainers/runc 1.4.0-rc.3, 1.3.3, 1.2.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/opencontainers/runc: affected <= 1.2.7; >= 1.3.0-rc.1, <= 1.3.2; >= 1.4.0-rc.1, <= 1.4.0-rc.2; fixed in 1.2.8, 1.3.3, 1.4.0-rc.3

## Suggested inspection (read-only)
- Go github.com/opencontainers/runc: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/opencontainers/runc.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9493-h29p-rfm2 (GitHub-reviewed advisory GHSA-9493-h29p-rfm2 lists affected ranges: Go github.com/opencontainers/runc >=0 =1.3.0-rc.1 =1.4.0-rc.1 <=1.4.0-rc.2)

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