CVE-2019-15879 in FreeBSD
Summary
by MITRE
In FreeBSD 12.1-STABLE before r356908, 12.1-RELEASE before p5, 11.3-STABLE before r356908, and 11.3-RELEASE before p9, a race condition in the cryptodev module permitted a data structure in the kernel to be used after it was freed, allowing an unprivileged process can overwrite arbitrary kernel memory.
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Analysis
by VulDB Data Team • 10/17/2020
The vulnerability identified as CVE-2019-15879 represents a critical race condition within the FreeBSD cryptodev module that exists across multiple versions of the operating system. This flaw specifically affects FreeBSD 12.1-STABLE prior to revision 356908, 12.1-RELEASE prior to patch 5, 11.3-STABLE prior to revision 356908, and 11.3-RELEASE prior to patch 9. The issue stems from improper synchronization mechanisms within the kernel's cryptographic device driver that governs hardware and software encryption operations.
The technical implementation of this vulnerability involves a classic use-after-free condition where kernel data structures remain accessible in memory even after they have been deallocated. This race condition occurs during concurrent access scenarios where multiple threads or processes attempt to manipulate the same cryptographic session or data structure simultaneously. The flaw allows an unprivileged user process to exploit this timing window to overwrite arbitrary kernel memory locations with controlled data. This type of vulnerability falls under the CWE-416 category for use-after-free conditions and represents a serious escalation path from user-space to kernel-space privileges.
The operational impact of CVE-2019-15879 is severe as it enables local privilege escalation attacks that can compromise the entire system. An attacker with minimal privileges can leverage this vulnerability to execute arbitrary code within kernel context, potentially gaining root access and full system control. The attack vector requires only local access to the system since the vulnerability exists in a kernel module that is accessible to all users. This makes it particularly dangerous in multi-user environments where untrusted users might have access to the system. The vulnerability aligns with ATT&CK technique T1068 which describes local privilege escalation through kernel exploits and T1059 which encompasses command and scripting interpreters that could be used to execute malicious code.
Mitigation strategies for this vulnerability include applying the official FreeBSD patches that address the race condition in the cryptodev module through proper synchronization mechanisms and memory management. System administrators should prioritize updating to the patched versions of FreeBSD 11.3-RELEASE p9, 12.1-RELEASE p5, or the corresponding stable releases containing revision 356908. Additionally, monitoring for suspicious kernel memory access patterns and implementing kernel address space layout randomization (KASLR) can provide defensive measures against exploitation attempts. The vulnerability demonstrates the critical importance of proper concurrency control in kernel modules and highlights the need for comprehensive testing of race conditions in security-critical system components. Organizations should also consider implementing least privilege principles and monitoring for unusual cryptographic operations that might indicate exploitation attempts.