CVE-2019-5603 in FreeBSD
Summary
by MITRE
In FreeBSD 12.0-STABLE before r350261, 12.0-RELEASE before 12.0-RELEASE-p8, 11.3-STABLE before r350263, 11.3-RELEASE before 11.3-RELEASE-p1, and 11.2-RELEASE before 11.2-RELEASE-p12, system calls operating on file descriptors as part of mqueuefs did not properly release the reference allowing a malicious user to overflow the counter allowing access to files, directories, and sockets opened by processes owned by other users.
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Analysis
by VulDB Data Team • 11/13/2023
The vulnerability described in CVE-2019-5603 represents a critical privilege escalation flaw within the FreeBSD operating system's message queue file system implementation. This issue affects multiple versions of FreeBSD including 12.0-STABLE, 11.3-STABLE, and 11.2-RELEASE, demonstrating the persistence of the flaw across different release branches. The vulnerability specifically targets the mqueuefs subsystem which provides a file system interface to POSIX message queues, creating an environment where improper reference counting can lead to serious security implications.
The technical root cause of this vulnerability lies in the improper release of references within system calls that operate on file descriptors within the mqueuefs. When processes interact with message queue file system objects, the reference counting mechanism fails to properly decrement counters, leading to a scenario where the reference counter can overflow. This overflow condition creates a situation where the system incorrectly maintains references to file descriptors, potentially allowing a malicious user to gain access to resources that should be restricted to other users. The flaw operates at the kernel level, making it particularly dangerous as it can be exploited to bypass normal access controls and privilege boundaries.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows attackers to access files, directories, and sockets that are owned by other processes. This creates a significant risk for system integrity and confidentiality, as unauthorized users could potentially read sensitive data, modify critical system files, or even establish persistent access to network sockets. The vulnerability essentially undermines the fundamental security model of the operating system by allowing users to manipulate file descriptor references in a way that violates normal process isolation mechanisms. This type of flaw can be leveraged to perform reconnaissance, escalate privileges, or even execute arbitrary code with elevated privileges, depending on the specific system configuration and available resources.
The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and more specifically relates to improper reference counting mechanisms that can lead to resource exhaustion and access control bypasses. From an attack perspective, this vulnerability maps to several MITRE ATT&CK techniques including privilege escalation through kernel exploits and access to files and resources. The exploitability of this vulnerability is enhanced by the fact that it requires minimal privileges to trigger, as it operates through legitimate system calls that are part of normal process behavior. Organizations should implement immediate mitigations including applying the relevant FreeBSD security patches, monitoring for unauthorized access attempts, and implementing additional access controls to limit the impact of potential exploitation.
The fix for this vulnerability involves correcting the reference counting implementation within the mqueuefs subsystem to ensure proper release of file descriptor references. This typically involves modifying the kernel code to properly decrement reference counters when file descriptors are closed or when system calls complete their operations. System administrators should prioritize updating to the patched versions of FreeBSD, specifically versions 12.0-RELEASE-p8, 11.3-RELEASE-p1, and 11.2-RELEASE-p12, which contain the necessary corrections to prevent the reference counter overflow condition. Additionally, organizations should conduct thorough security assessments to identify any potential exploitation attempts and ensure that their monitoring systems are configured to detect unusual access patterns that might indicate exploitation of this vulnerability.