CVE-2026-40599: ClearanceKit Privilege Escalation Flaw

CVE-2026-40599 Overview

CVE-2026-40599 is an authorization bypass vulnerability in ClearanceKit, a macOS security component that intercepts file-system access events and enforces per-process access policies. Prior to version 5.0.5, ClearanceKit incorrectly treats a process with an empty Team ID and a non-empty Signing ID as an Apple platform binary. This flaw allows malicious software to impersonate an Apple process in the global allowlist and gain unauthorized access to all protected files on the system.

Critical Impact

Malicious software can bypass ClearanceKit's file access controls by exploiting improper code signing validation, enabling unauthorized access to protected files and sensitive data.

Affected Products

• ClearanceKit versions prior to 5.0.5
• macOS systems utilizing ClearanceKit for file-system access control

Discovery Timeline

• 2026-04-21 - CVE-2026-40599 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-40599

Vulnerability Analysis

This vulnerability stems from CWE-863 (Incorrect Authorization), where ClearanceKit fails to properly validate code signing credentials when determining whether a process should be trusted as an Apple platform binary. The core issue lies in how ClearanceKit interprets the combination of an empty Team ID with a non-empty Signing ID.

Apple platform binaries are typically signed with Apple's own certificates and have specific code signing attributes. ClearanceKit maintains a global allowlist that grants Apple platform binaries unrestricted access to protected files. However, the flawed validation logic allows an attacker to craft a malicious process that appears to meet the criteria for Apple platform binary status without actually being signed by Apple.

When a process presents an empty Team ID alongside a non-empty Signing ID, ClearanceKit incorrectly interprets this as a valid Apple platform binary signature pattern. This allows the malicious process to inherit all the file-system access privileges normally reserved for legitimate Apple system processes.

Root Cause

The root cause is improper authorization logic in ClearanceKit's code signing validation routine. The software fails to properly distinguish between legitimate Apple platform binaries and processes that deliberately manipulate their code signing attributes to appear as Apple binaries. Specifically, the validation does not adequately verify that the Signing ID corresponds to a valid Apple certificate chain when the Team ID is empty.

Attack Vector

The attack requires local access to the macOS system where ClearanceKit is installed. An attacker with the ability to execute code on the target system can create a malicious process with specially crafted code signing attributes—specifically an empty Team ID combined with a non-empty Signing ID. When this process requests access to protected files, ClearanceKit's flawed validation logic grants the request, treating the malicious process as a trusted Apple platform binary.

This effectively allows the attacker to:

• Access files protected by ClearanceKit's access control policies
• Read sensitive user data and system files
• Bypass security boundaries established by ClearanceKit

The attack does not require user interaction beyond the initial execution of the malicious software. For technical details regarding the vulnerability mechanism, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-40599

Indicators of Compromise

• Processes running on the system with empty Team IDs but non-empty Signing IDs accessing protected files
• Unusual file access patterns to ClearanceKit-protected directories from unexpected processes
• Processes not signed by Apple attempting to access system-protected resources

Detection Strategies

• Monitor code signing validation events for processes with anomalous Team ID and Signing ID combinations
• Implement endpoint detection rules to flag processes with empty Team IDs accessing protected file system locations
• Review ClearanceKit logs for access grants to processes that do not match known Apple platform binary signatures

Monitoring Recommendations

• Enable verbose logging in ClearanceKit to capture detailed information about file access authorization decisions
• Deploy behavioral analysis to detect processes mimicking Apple platform binary attributes
• Establish baseline of legitimate Apple processes on endpoints and alert on deviations

How to Mitigate CVE-2026-40599

Immediate Actions Required

• Upgrade ClearanceKit to version 5.0.5 or later immediately
• Audit systems for any indicators of compromise related to this vulnerability
• Review file access logs to identify any unauthorized access to protected files

Patch Information

The vulnerability has been addressed in ClearanceKit version 5.0.5. The fix corrects the code signing validation logic to properly verify that processes claiming Apple platform binary status are genuinely signed by Apple. Organizations should update to this version through their standard software deployment processes. Additional details are available in the GitHub Security Advisory.

Workarounds

• Implement additional access controls at the operating system level to restrict sensitive file access until patching is complete
• Use application allowlisting solutions to prevent execution of unsigned or improperly signed applications
• Consider temporarily restricting execution of new applications on critical systems until the patch is deployed