PMC Monitoring Bypass in FreeBSD Kernel

Executive Summary

This vulnerability involves a flaw in the hwpmc(4) component of FreeBSD. When a process executes a setuid or setgid binary using execve(2), the system is supposed to detach Performance Monitoring Counters (PMCs) owned by unprivileged processes. However, an inverted check prevents this detachment, allowing unprivileged local users to continue monitoring processes even after they execute privileged binaries.

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Detection Guidance

This vulnerability is specific to FreeBSD systems using the hwpmc(4) driver. Detection primarily involves checking if the hwpmc module is loaded and if the system is vulnerable. Run 'kldstat | grep hwpmc' to check if hwpmc is loaded. If loaded, verify if your system is patched by checking the FreeBSD version against the advisory.

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Impact Analysis

An attacker with local access could exploit this to monitor sensitive processes after privilege escalation, potentially leaking confidential information or enabling further attacks by observing program behavior or data access patterns.

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Compliance Impact

This vulnerability could potentially impact compliance with standards requiring strict process isolation and privileged access controls, such as HIPAA for protected health information or GDPR for data processing. The flaw allows unauthorized monitoring of privileged processes, which may violate confidentiality requirements in these regulations.

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Mitigation Strategies

Apply the vendor-supplied patch or update for FreeBSD systems to fix the inverted check in hwpmc(4). Disable PMC monitoring for unprivileged processes until patched.

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