CVE-2024-23653: Mobyproject BuildKit Privilege Escalation

CVE-2024-23653 Overview

CVE-2024-23653 is a critical authorization bypass vulnerability in BuildKit, a toolkit developed by the Moby Project for converting source code to build artifacts. The vulnerability exists in BuildKit's APIs for running interactive containers based on built images. Attackers can exploit these APIs to run containers with elevated privileges, bypassing the security.insecure entitlement checks that normally require explicit configuration and user permission.

Critical Impact

This vulnerability allows unauthorized privilege escalation through BuildKit's interactive container APIs, potentially enabling attackers to execute containers with elevated privileges without proper authorization, leading to complete compromise of confidentiality, integrity, and availability.

Affected Products

• Mobyproject BuildKit versions prior to v0.12.5

Discovery Timeline

• 2024-01-31 - CVE-2024-23653 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-23653

Vulnerability Analysis

This vulnerability is classified under CWE-863 (Incorrect Authorization), indicating a fundamental flaw in how BuildKit validates authorization for privileged container operations. BuildKit provides APIs that allow running interactive containers based on images created during the build process. Under normal circumstances, running containers with elevated privileges requires the security.insecure entitlement to be explicitly enabled in both the buildkitd daemon configuration and approved by the user initiating the build request.

The vulnerability allows attackers to circumvent these authorization controls entirely. By crafting specific API requests, an attacker can instruct BuildKit to execute a container with elevated privileges without having the required entitlements configured or approved. This effectively bypasses the security model designed to prevent unauthorized privilege escalation.

Root Cause

The root cause of this vulnerability lies in improper authorization validation within BuildKit's interactive container API handlers. The code path that processes requests to run interactive containers failed to properly enforce the security.insecure entitlement checks before executing privileged container operations. This authorization bypass allows attackers to escalate privileges by exploiting the gap between the intended security policy and its actual enforcement.

Attack Vector

The attack vector for CVE-2024-23653 is network-based and requires no user interaction or prior authentication. An attacker with network access to a vulnerable BuildKit instance can exploit this vulnerability through the following mechanism:

1. The attacker identifies a BuildKit instance exposed over the network
2. Using BuildKit's APIs for running interactive containers, the attacker crafts a request that specifies elevated privileges
3. Due to the authorization bypass, BuildKit processes the request without verifying that the security.insecure entitlement is properly configured
4. The container executes with elevated privileges, allowing the attacker to perform actions that should be restricted

The vulnerability is particularly dangerous when BuildKit instances are accessible from untrusted networks or when processing build requests from untrusted frontend sources.

Detection Methods for CVE-2024-23653

Indicators of Compromise

• Unexpected containers running with elevated privileges or --privileged flags on systems using BuildKit
• Build logs showing interactive container sessions that were not initiated by authorized users
• API requests to BuildKit that specify privileged execution without corresponding entitlement configurations
• Anomalous network connections to BuildKit daemon ports from unexpected sources

Detection Strategies

• Monitor BuildKit daemon logs for API calls related to interactive container execution, particularly those requesting elevated privileges
• Implement network monitoring to detect unauthorized access attempts to BuildKit API endpoints
• Audit container runtime logs for containers spawned with privileged capabilities that bypass entitlement verification
• Deploy runtime security tools to detect privilege escalation attempts within the container environment

Monitoring Recommendations

• Enable verbose logging on buildkitd to capture detailed API request information
• Set up alerts for any container execution requests that include privilege escalation parameters
• Monitor for BuildKit versions prior to v0.12.5 across the infrastructure using vulnerability scanning tools
• Implement network segmentation to restrict access to BuildKit APIs from trusted sources only

How to Mitigate CVE-2024-23653

Immediate Actions Required

• Upgrade BuildKit to version v0.12.5 or later immediately to address this vulnerability
• Restrict network access to BuildKit APIs using firewall rules and network segmentation until patching is complete
• Audit existing BuildKit configurations and logs for signs of exploitation
• Avoid using BuildKit frontends from untrusted sources

Patch Information

The Moby Project has released BuildKit version v0.12.5 which contains the security fix for this vulnerability. The fix is documented in GitHub Pull Request #4602 and the patched release is available at the BuildKit v0.12.5 Release Page. For complete technical details about the vulnerability and the fix, refer to the GitHub Security Advisory GHSA-wr6v-9f75-vh2g.

Workarounds

• Isolate BuildKit instances from untrusted networks and restrict API access to authorized systems only
• Implement strict network policies to prevent unauthorized clients from reaching BuildKit endpoints
• Avoid using BuildKit frontends from untrusted or unverified sources until the upgrade is applied
• Monitor container runtime for any privileged container executions that were not explicitly authorized

# Configuration example: Restrict BuildKit daemon to localhost only
# In buildkitd configuration, bind to localhost instead of all interfaces
buildkitd --addr tcp://127.0.0.1:1234

# Use firewall rules to restrict access to BuildKit port
iptables -A INPUT -p tcp --dport 1234 -s trusted_network_cidr -j ACCEPT
iptables -A INPUT -p tcp --dport 1234 -j DROP