CVE-2019-5596 in FreeBSD
Summary
by MITRE
In FreeBSD 11.2-STABLE after r338618 and before r343786, 12.0-STABLE before r343781, and 12.0-RELEASE before 12.0-RELEASE-p3, a bug in the reference count implementation for UNIX domain sockets can cause a file structure to be incorrectly released potentially allowing a malicious local user to gain root privileges or escape from a jail.
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Analysis
by VulDB Data Team • 07/12/2024
This vulnerability exists in FreeBSD operating systems within specific version ranges and represents a critical reference count management flaw in the UNIX domain socket implementation. The issue stems from improper handling of reference counts for file structures, which creates a race condition scenario that can lead to use-after-free conditions. When multiple processes interact with UNIX domain sockets, the kernel fails to properly maintain the reference count for underlying file structures, potentially allowing an attacker to manipulate these references and cause premature deallocation of critical kernel memory objects. This fundamental flaw in the kernel's memory management system creates a pathway for privilege escalation and sandbox escape.
The technical implementation of this vulnerability involves the interaction between the socket subsystem and the file descriptor management within the FreeBSD kernel. During normal operation, when UNIX domain sockets are created and used, the kernel maintains reference counts to track how many processes are actively using a particular file structure. However, due to a specific bug in the reference counting logic between revisions r338618 and r343786 for FreeBSD 11.2-STABLE, and similarly in 12.0-STABLE before r343781, the reference count decrement operations do not properly synchronize with concurrent access patterns. This creates a window where a malicious local user can exploit the race condition to force the release of a file structure while it is still being accessed, leading to memory corruption that can be leveraged for privilege escalation.
The operational impact of this vulnerability is severe as it allows a local attacker to potentially gain root privileges or escape from a jail environment. The use-after-free condition can be exploited through carefully crafted socket operations that manipulate the reference counting behavior to cause controlled memory corruption. Attackers can leverage this vulnerability to execute arbitrary code with kernel-level privileges, effectively bypassing the security model that separates user processes from system-level operations. The vulnerability affects systems running FreeBSD 11.2-STABLE, 12.0-STABLE, and 12.0-RELEASE versions before specific patch releases, making it particularly concerning for systems that have not been updated to the patched versions.
This vulnerability aligns with CWE-415, which describes improper double-free conditions, and CWE-416, which covers use-after-free conditions in memory management. The attack pattern follows techniques described in the MITRE ATT&CK framework under T1068, which covers local privilege escalation, and T1197, which covers exploit for privilege escalation through kernel vulnerabilities. The exploitation requires local access to the system and involves manipulating concurrent socket operations to trigger the race condition. Organizations should implement immediate patching strategies and monitor for potential exploitation attempts, as this vulnerability represents a significant threat to system integrity and security boundaries. The fix involves correcting the reference counting implementation in the socket subsystem to ensure proper synchronization and prevent premature deallocation of file structures during concurrent access scenarios.