CVE-2026-34040: Moby Authorization Bypass Vulnerability

CVE-2026-34040 Overview

CVE-2026-34040 is an authorization bypass vulnerability affecting Moby, the open source container framework that powers Docker. Prior to version 29.3.1, a security flaw allows attackers to bypass authorization plugins (AuthZ), potentially enabling unauthorized access to container operations and Docker daemon functionality. This vulnerability is classified under CWE-288 (Authentication Bypass Using an Alternate Path or Channel).

Critical Impact
Attackers with local access can bypass AuthZ plugins to perform unauthorized container operations, potentially leading to complete compromise of the container environment and host system.

Affected Products

Moby (Docker Engine) versions prior to 29.3.1
Docker installations using AuthZ plugins for access control
Container environments relying on authorization plugins for security enforcement

Discovery Timeline

2026-03-31 - CVE-2026-34040 published to NVD
2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-34040

Vulnerability Analysis

This vulnerability enables attackers to circumvent the authorization plugin mechanism in Moby/Docker Engine. Authorization plugins (AuthZ) are critical security components that control access to Docker daemon operations, allowing administrators to implement fine-grained access control policies. When this bypass is exploited, the security controls implemented through AuthZ plugins become ineffective, allowing unauthorized users to execute privileged container operations.

The local attack vector requires the attacker to have some level of access to the system running the vulnerable Docker daemon. With low privileges and no user interaction required, an attacker can exploit this flaw to gain elevated access beyond their intended authorization scope. The scope change indicator means this vulnerability can affect resources beyond the vulnerable component itself, potentially impacting the host system and other containers.

Root Cause

The root cause stems from an authentication bypass vulnerability (CWE-288) where an alternate path or channel exists that allows requests to bypass the normal authorization plugin validation flow. This enables attackers to send requests that evade the AuthZ plugin checks entirely, circumventing the intended security controls.

Attack Vector

The attack leverages local access to the Docker environment. An attacker with basic local access can craft requests that bypass the AuthZ plugin validation mechanism, effectively gaining unauthorized access to Docker daemon operations. This could allow:

Unauthorized container creation, modification, or deletion
Access to sensitive container data and volumes
Execution of commands within privileged containers
Potential container escape leading to host compromise

The vulnerability does not require user interaction and can be exploited with low attack complexity, making it a significant risk for environments relying on AuthZ plugins for security enforcement.

Detection Methods for CVE-2026-34040

Indicators of Compromise

Unexpected container operations performed by users without proper AuthZ permissions
Docker daemon logs showing API calls that should have been blocked by AuthZ plugins
Unusual container creation, modification, or privileged operations from low-privilege accounts
AuthZ plugin logs showing inconsistencies between expected denials and actual allowed operations

Detection Strategies

Monitor Docker daemon logs for API requests that bypass expected authorization controls
Implement audit logging for all Docker daemon operations and correlate with AuthZ plugin decisions
Deploy runtime container security monitoring to detect unauthorized container activities
Review Docker API access patterns for anomalies indicating authorization bypass attempts

Monitoring Recommendations

Enable verbose logging for AuthZ plugins to track all authorization decisions
Implement alerting for privileged container operations from unexpected sources
Monitor for Docker daemon restarts or configuration changes that might disable AuthZ
Track container escape indicators and host access from container contexts

How to Mitigate CVE-2026-34040

Immediate Actions Required

Upgrade Moby/Docker Engine to version 29.3.1 or later immediately
Audit recent Docker daemon activity for signs of unauthorized operations
Review and restrict local access to systems running Docker daemons
Implement network segmentation to limit exposure of Docker daemon endpoints

Patch Information

This vulnerability has been patched in Moby version 29.3.1. The fix addresses the authorization bypass by ensuring all requests properly traverse the AuthZ plugin validation flow. Refer to the GitHub Docker Release Notes for complete release details and the GitHub Security Advisory GHSA-x744-4wpc-v9h2 for technical vulnerability information.

Workarounds

Restrict local access to Docker daemon hosts to trusted users only
Implement additional access controls at the network and host level independent of AuthZ plugins
Consider temporarily disabling non-essential Docker operations until patching is complete
Deploy host-based intrusion detection to monitor for suspicious container activities

bash

# Upgrade Docker Engine to patched version
# For Debian/Ubuntu systems:
sudo apt-get update
sudo apt-get install docker-ce=5:29.3.1-1~ubuntu.22.04~jammy docker-ce-cli=5:29.3.1-1~ubuntu.22.04~jammy

# Verify installed version
docker --version

# Review AuthZ plugin configuration
docker info | grep -i auth