Vulnerability Database

347,940

Total vulnerabilities in the database

CVE-2026-42306 — github.com/docker/docker

Time-of-check Time-of-use (TOCTOU) Race Condition

Summary

A race condition during docker cp mount setup allows a malicious container to redirect a bind mount target to an arbitrary host path, potentially overwriting host files or causing denial of service.

Details

When copying files into a container, the daemon sets up a temporary filesystem view by bind-mounting volumes into a private mount namespace. During this setup, the mount destination is created inside the container root and then a bind mount is attached using the container-relative path resolved to an absolute host path.

Between mountpoint creation and the mount() syscall, a process running inside the container can replace the destination (or a parent path component) with a symlink pointing to an arbitrary location on the host. The mount() syscall follows the symlink, causing the volume to be bind-mounted onto an arbitrary host path instead of the intended container path.

Impact

A malicious container can redirect a volume bind mount to an arbitrary host path. The impact depends on the volume content and mount options:

  • If the volume is writable, arbitrary host files at the redirected path could be overwritten with the volume's contents.
  • If the volume is read-only, the host path is masked by the mount for the duration of the operation, causing denial of service.
  • In all cases the mount is temporary (torn down after the docker cp completes), but the effects of any writes persist.

Conditions for exploitation

  • A container must have at least one volume mount.
  • A process inside the container must be able to rapidly create and swap symlinks at the volume mount destination path.
  • An operator must initiate a docker cp into that container, or call the PUT /containers/{id}/archive or HEAD /containers/{id}/archive API endpoints.

Not affected

  • Containers that do not have volume mounts are not affected, as the race occurs during volume bind-mount setup.

Workarounds

  • Only run containers from trusted images.
  • Avoid using docker cp with untrusted running containers.
  • Use authorization plugins to restrict access to the archive API endpoints (PUT /containers/{id}/archive, HEAD /containers/{id}/archive).

CVSS v3:

  • Severity: Unknown
  • Score:
  • AV:L/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:H

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.