# CVE-2026-15788: WCOW cache mount source selector resolves NTFS junctions outside of cache root

> An attacker can read arbitrary host files via NTFS junctions in BuildKit cache mounts on Windows Container on Windows workers.

- **Severity:** Medium 5.6 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 20 Jul 2026
- **Updated:** 21 Jul 2026
- **Also known as:** GHSA-388v-wmr2-g2v2

## What is CVE-2026-15788?

CVE-2026-15788 is a medium-severity path traversal vulnerability in moby BuildKit, published on 20 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

BuildKit's cache mount source= selector on Windows Container on Windows (WCOW) workers does not detect NTFS directory junctions placed inside the cache root. A build authored by an untrusted user on a WCOW-configured BuildKit daemon can read arbitrary host files reachable to the BuildKit daemon process.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2026-15788?

It affects 1 product.


Products: Mobyproject Buildkit.

## How do I fix CVE-2026-15788?

Apply the vendor's patch.

## Is CVE-2026-15788 being exploited?

There is no known exploitation of CVE-2026-15788 in the wild and no public exploit code.

## Other vulnerabilities in moby BuildKit

- [CVE-2024-23652](https://insights.sbomify.com/CVE-2024-23652/): BuildKit possible host system access from mount stub cleaner (critical 10.0)
- [CVE-2024-23653](https://insights.sbomify.com/CVE-2024-23653/): BuildKit interactive containers API does not validate entitlements check (critical 9.8)
- [CVE-2024-23651](https://insights.sbomify.com/CVE-2024-23651/): BuildKit possible race condition with accessing subpaths from cache mounts (high 8.7)
- [CVE-2026-33747](https://insights.sbomify.com/CVE-2026-33747/): BuildKit vulnerable to malicious frontend causing file escape outside of storage root (high 8.4)
- [CVE-2026-33748](https://insights.sbomify.com/CVE-2026-33748/): BuildKit Git URL subdir component can cause access to restricted files (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-15788 and fix it if it is affected.

What it is: CVE-2026-15788 is a medium-severity path traversal vulnerability in moby BuildKit, published on 20 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-15788 in the wild and no public exploit code.

Affected product: moby BuildKit. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-15788/ (Markdown: https://insights.sbomify.com/CVE-2026-15788/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15788
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15788
- OSV: https://osv.dev/vulnerability/CVE-2026-15788

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-15788/
Summaries are generated and may contain mistakes; the official description above is the record.