# CVE-2026-15788: Moby BuildKit arbitrary file read via NTFS junctions in WCOW cache mount

Source: https://junglewise.ai/threats/cve-2026-15788-moby-buildkit-arbitrary-file-read-via-ntfs-junctions-in-wcow  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-20. Updated: 2026-07-20  
License: CC BY 4.0 with a link back

CVE-2026-15788 · Severity: info · CVSS 5.6 · Published 2026-07-20

Moby BuildKit, a tool used for building container images, contains a vulnerability when running on Windows. An untrusted user can craft a build process that bypasses security boundaries to read sensitive files from the host computer. This could lead to the exposure of private data or system configuration files reachable by the BuildKit service.

Technologies: [Moby Project BuildKit](https://junglewise.ai/threats/technologies/buildkit). Vendors: [Moby Project](https://junglewise.ai/threats/vendors/moby-project).

## Quick answers

**Is CVE-2026-15788 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-15788 being exploited in the wild.

**How severe is CVE-2026-15788?** Informational severity, with a CVSS score of 5.6, published 20 July 2026.

**Which products and versions are affected?** Moby Project BuildKit < 0.31.2.

**Is there a fix for CVE-2026-15788?** A patch was published on 2026-07-20: Fix available in version 0.31.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-15788 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-15788?** Check whether you run Moby Project BuildKit at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in BuildKit's cache mount 'source=' selector when used on Windows Container on Windows (WCOW) workers. The component fails to properly detect or validate NTFS directory junctions (symbolic links) placed within the cache root. An attacker providing a malicious build definition can use these junctions to point to locations outside the intended cache directory. This allows the build process to read any file on the host system that the BuildKit daemon process has permissions to access. The issue is tracked as CWE-59 and is resolved in BuildKit version 0.31.2.

## Affected products

- Moby BuildKit < 0.31.2

## Timeline

- 2026-07-16: advisory: GitHub Security Advisory published by Moby project
- 2026-07-20: disclosed: NVD publication date
- 2026-07-20: patched: Fix available in version 0.31.2

## References

- [https://github.com/moby/buildkit/security/advisories/GHSA-388v-wmr2-g2v2](https://github.com/moby/buildkit/security/advisories/GHSA-388v-wmr2-g2v2)

## Related threats

- [BuildKit daemon panic when CDI disabled flag is used](https://junglewise.ai/threats/cve-2026-93316-if-buildkit-daemon-is-started-with-cdi-disabled-it-can-lead-to)
- [Moby BuildKit command injection in Git source checkout](https://junglewise.ai/threats/cve-2026-15793-moby-buildkit-command-injection-in-git-source-checkout)
- [Moby BuildKit path traversal in low-level build API](https://junglewise.ai/threats/cve-2026-15791-moby-buildkit-path-traversal-in-low-level-build-api)
- [Moby BuildKit path traversal in local source upload](https://junglewise.ai/threats/cve-2026-15789-moby-buildkit-path-traversal-in-local-source-upload)