CVE-2026-41568: Docker & Moby Race Condition in docker cp Mount Setup

Technical summary

CVE-2026-41568 is a time-of-check-time-of-use (TOCTOU) race condition in the docker cp mount initialization sequence. When copying files between containers and hosts, the daemon performs security checks before finalizing mount paths. A malicious container can exploit the window between validation and mount completion to manipulate symlinks or filesystem state, redirecting writes to unintended absolute paths on the host. The vulnerability stems from insufficient synchronization during the mount setup phase, allowing directory traversal despite intended path restrictions.

Business impact

Organizations running Docker or Moby-based container platforms face host filesystem integrity risks. An insider or compromised container could create denial-of-service conditions by filling critical directories, corrupt configuration files, or establish persistence mechanisms outside container boundaries. Multi-tenant environments and CI/CD platforms where untrusted images are executed face elevated exposure. The impact is localized to the affected host and requires container execution privileges, but successful exploitation could disrupt service availability or enable lateral movement.

Affected systems

Docker Engine versions prior to 29.5.1, Docker Daemon versions 28.5.2 and earlier, and Moby Daemon versions before 2.0.0-beta.14 are vulnerable. Organizations should identify running instances via docker version and moby version commands. Verify the exact installed versions against vendor advisories, as patching schedules vary between Docker Enterprise, Community editions, and independent Moby deployments.

Exploitability

Exploitation requires local container access and relies on precise timing to win a race condition, making it moderately difficult but not infeasible. The attack does not require elevated privileges within the container, only ability to execute the docker cp command or trigger it via exposed APIs. User interaction is necessary (the CVSS vector reflects PR:L and UI:R), meaning the attack requires a user to perform a copy operation while the malicious container manipulates the filesystem. Detection and execution of reliable exploits is non-trivial due to race condition variability, but proven proof-of-concepts are likely to emerge post-disclosure.

Remediation

Patch Docker Engine to version 29.5.1 or later, upgrade Moby Daemon to 2.0.0-beta.14 or newer, and ensure Docker Daemon is at version 28.5.3 or above. Review deployment manifests to enforce image scanning and prevent execution of untrusted container images. Consider runtime policies restricting docker cp to trusted workflows and monitor for suspicious copy operations targeting host paths.

Patch guidance

Apply Docker Engine version 29.5.1 or later as the primary remediation. For Moby deployments, upgrade to version 2.0.0-beta.14 or later. For Docker Daemon, verify that version 28.5.3 or above is deployed—versions 28.5.2 and prior are vulnerable. Test patches in non-production environments before rollout to confirm compatibility with existing container workloads and orchestration configurations. Confirm successful patching by running 'docker version' and verifying the Engine version number matches the patched release.

Detection guidance

Monitor container runtime logs for unexpected docker cp operations targeting host root or system directories. Implement filesystem integrity monitoring (FIM) on hosts to detect unauthorized file creation in sensitive paths. Watch for failed docker cp attempts with permission errors, which may indicate exploitation attempts. Correlate container execution logs with host syscall traces to identify timing anomalies during mount operations. Organizations using container security platforms should enable runtime anomaly detection rules for suspicious copy operations.

Why prioritize this

Medium severity (CVSS 6.1) is appropriate given the moderate exploitability barriers (race condition timing, local access requirement) and significant availability and integrity impacts. The vulnerability is not yet in active exploitation at scale (KEV status: not currently listed), but race condition vulnerabilities are difficult to predict and can be weaponized with sufficient engineering effort. Prioritize patching for multi-tenant environments, CI/CD platforms executing external images, and systems where container-to-host file operations are routine. Organizations with strict container image controls and isolated single-tenant deployments can schedule patching in regular maintenance windows.

Risk score, explained

The CVSS 3.1 score of 6.1 reflects low attack vector (local-only), high attack complexity (race condition requires timing precision), low privileges required (container user suffices), and required user interaction (copy operation must be initiated). Impact is constrained to integrity (file creation) and availability (potential denial-of-service via filesystem exhaustion), with no confidentiality breach. The score appropriately elevates due to the scope change (S:C) from container to host context, indicating cross-boundary impact despite limited initial access.

Frequently asked questions