CVE-2026-33997: Moby Privilege Escalation Vulnerability

CVE-2026-33997 Overview

A security vulnerability has been identified in Moby, the open source container framework that powers Docker. This Authorization Bypass vulnerability allows the privilege validation mechanism to be bypassed during docker plugin install operations. Due to an error in the daemon's privilege comparison logic, the daemon may incorrectly accept a privilege set that differs from the one approved by the user, potentially allowing malicious plugins to gain unauthorized capabilities.

Critical Impact

Attackers could install Docker plugins with elevated privileges beyond what users approve, potentially leading to container escape scenarios, unauthorized host access, or compromise of container orchestration environments.

Affected Products

• Moby (Docker) versions prior to 29.3.1
• Docker Engine installations using the plugin system
• Container environments with plugin installation capabilities enabled

Discovery Timeline

• 2026-03-31 - CVE-2026-33997 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-33997

Vulnerability Analysis

This vulnerability is classified as CWE-193 (Off-by-one Error), which occurs in the daemon's privilege comparison logic during Docker plugin installation. The flaw manifests in how the Docker daemon validates plugin privileges against user-approved permissions.

When a user installs a Docker plugin, they are typically presented with the plugin's requested privileges and must approve them. However, due to the comparison logic error, the daemon fails to properly verify that the actual privileges match the approved set. This creates a dangerous gap where a plugin could request and receive privileges that were never explicitly authorized by the user.

A particularly concerning aspect of this vulnerability is that plugins requesting exactly one privilege bypass privilege comparison entirely, as no validation is performed in this edge case. This makes single-privilege plugins especially dangerous attack vectors.

Root Cause

The root cause lies in an off-by-one error (CWE-193) within the privilege comparison function of the Docker daemon. This type of error typically occurs when loop boundaries or array indices are incorrectly calculated, causing one fewer or one more iteration than intended. In this case, the comparison logic appears to skip or incorrectly process privilege entries, allowing discrepancies between approved and actual privileges to go undetected.

Attack Vector

The vulnerability requires network access and user interaction, as an attacker would need to:

1. Create a malicious Docker plugin that requests elevated privileges
2. Convince a user to install the plugin (social engineering component)
3. Exploit the comparison logic flaw to gain privileges beyond what the user approved

The attack could be facilitated through compromised plugin registries, typosquatting attacks on popular plugin names, or supply chain compromises where legitimate plugins are modified to include malicious privilege requests.

Detection Methods for CVE-2026-33997

Indicators of Compromise

• Unexpected Docker plugins installed with elevated privileges not matching user approval records
• Plugin installation audit logs showing privilege discrepancies
• Containers or plugins with capabilities that exceed documented requirements
• Anomalous system calls or host resource access from plugin containers

Detection Strategies

• Review Docker daemon logs for plugin installation events and compare requested vs. granted privileges
• Implement runtime security monitoring to detect plugins accessing resources beyond their stated scope
• Audit installed plugins using docker plugin ls and verify their privilege configurations
• Deploy container security platforms that monitor for privilege escalation attempts

Monitoring Recommendations

• Enable Docker daemon debug logging to capture detailed plugin installation events
• Configure alerting for new plugin installations in production environments
• Implement continuous monitoring of container capabilities and seccomp profiles
• Regularly audit plugin privileges against a known-good baseline

How to Mitigate CVE-2026-33997

Immediate Actions Required

• Upgrade Moby/Docker Engine to version 29.3.1 or later immediately
• Audit all currently installed plugins and their granted privileges
• Temporarily disable plugin installation capabilities in production environments if upgrading is delayed
• Review recent plugin installation logs for potential exploitation

Patch Information

The Moby project has released version 29.3.1 which addresses this vulnerability. The fix corrects the privilege comparison logic to ensure proper validation of all plugin privilege requests, including the edge case where plugins request exactly one privilege.

For detailed release information, see the GitHub Release Notes. Additional technical details are available in the GitHub Security Advisory.

Workarounds

• Restrict plugin installation permissions to trusted administrators only
• Implement policy enforcement to block plugin installations until patching is complete
• Use Docker's authorization plugins to add additional privilege validation layers
• Deploy network segmentation to limit exposure of Docker daemon endpoints

# Configuration example - Restrict Docker plugin capabilities
# Add to /etc/docker/daemon.json to disable live restore and limit plugin scope
{
  "authorization-plugins": ["your-authz-plugin"],
  "no-new-privileges": true
}

# Verify installed plugins and their privileges
docker plugin ls --format '{{.Name}}: {{.Enabled}}'

# Disable suspicious plugins pending investigation
docker plugin disable <plugin-name>