ClearanceKit CVE-2026-40604

Exploitation requires the attacker to have already achieved root (UID 0) privileges on the target macOS system where ClearanceKit opfilter extension is running. The attacker must be able to send signals (SIGSTOP, SIGKILL, or SIGTERM) to the opfilter process, which requires root authority. ClearanceKit must be actively installed and configured to enforce file-access policies - if ClearanceKit is not deployed or is already disabled, there is no security control to bypass. The vulnerability affects default configurations of ClearanceKit prior to version 5.0.6 and does not require any specific ClearanceKit policy configuration or non-standard macOS settings. Limiting factors: macOS System Integrity Protection (SIP) does not prevent root from signaling user-space Endpoint Security extensions. The prerequisite root access means this is effectively a post-exploitation technique rather than an initial compromise vector, which significantly reduces the pool of real-world attack scenarios where this vulnerability would be the critical link in an attack chain.

This vulnerability presents a paradoxical risk profile requiring careful assessment. The CVSS base score of 8.2 is elevated due to the scope change and complete bypass of ClearanceKit's security controls. However, exploitation requires pre-existing root access (PR:H), which already represents full system compromise on most macOS configurations. The critical question for defenders is: does ClearanceKit provide defense-in-depth against a root-compromised system, or protect against privilege escalation pathways? If ClearanceKit is deployed to enforce mandatory access controls that should survive even root compromise (defense against malicious root processes, separation of administrative duties, or compliance requirements), this is a critical bypass. If ClearanceKit primarily protects against pre-root threats, the practical risk is lower since the attacker already has effective control. The local-only attack vector (AV:L) and high privilege requirement (PR:H) significantly limit exposure compared to network-accessible vulnerabilities. No EPSS, KEV, or POC data is available, suggesting no widespread exploitation. SSVC assessment: exploitation is straightforward for a skilled attacker with root access (low complexity), technical impact is high (complete security control bypass), but automatable exploitation across diverse environments is limited by the prerequisite root access. Priority depends entirely on your threat model for root-level compromise - organizations using ClearanceKit as a control against malicious insiders with administrative access should treat this as high priority; others may defer to normal patching cycles.

An attacker who has achieved root access on a macOS system protected by ClearanceKit (through separate vulnerability exploitation, stolen credentials, or malicious insider activity) executes 'kill -STOP $(pgrep -f uk.craigbass.clearancekit.opfilter)' to suspend the ClearanceKit Endpoint Security extension. With the extension suspended, all file-access authorization events time out and default to allow. The attacker now accesses sensitive files or modifies protected system components that ClearanceKit policies would normally block, completely bypassing the intended access restrictions while leaving minimal forensic evidence since the bypass occurs silently through legitimate signal mechanisms. The attacker can resume the extension later with SIGCONT to restore normal operation and avoid detection.