CVE-2017-1088 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.1-STABLE, 11.1-RELEASE-p4, 11.0-RELEASE-p15, 10.4-STABLE, 10.4-RELEASE-p3, and 10.3-RELEASE-p24, the kernel does not properly clear the memory of the kld_file_stat structure before filling the data. Since the structure filled by the kernel is allocated on the kernel stack and copied to userspace, a leak of information from the kernel stack is possible. As a result, some bytes from the kernel stack can be observed in userspace.
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Analysis
by VulDB Data Team • 01/24/2021
This vulnerability represents a classic kernel information disclosure flaw that affects multiple versions of the FreeBSD operating system. The issue stems from improper memory handling within the kernel's module loading subsystem, specifically when processing the kld_file_stat structure through the kldstat system call. The vulnerability exists in the kernel's memory management routines where the kld_file_stat structure is allocated on the kernel stack but not properly cleared before being populated with data. This memory clearance failure creates a situation where sensitive data remnants from previous kernel operations persist in memory locations that are subsequently exposed to userspace applications.
The technical implementation of this vulnerability involves the kernel's handling of the kldstat system call which is used to retrieve information about loaded kernel modules. When a process calls kldstat, the kernel allocates a kld_file_stat structure on its stack to hold module statistics. However, the kernel fails to zero out this structure before populating it with actual module data, leaving behind uninitialized memory contents from previous kernel operations. Since this structure is then copied to userspace, any data that remained in memory locations after the structure's allocation becomes accessible to unprivileged users, creating a potential information leak.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially expose sensitive kernel memory contents that might include cryptographic keys, session tokens, or other confidential data that was previously stored in the kernel stack. This information leak can be exploited by malicious users to gather intelligence about the system's internal state, potentially aiding in more sophisticated attacks. The vulnerability affects a wide range of FreeBSD versions, making it particularly concerning for systems that have not been updated to the patched releases. According to CWE classification, this corresponds to CWE-248, which addresses the exposure of uninitialized memory, while the ATT&CK framework would categorize this under privilege escalation techniques through information gathering.
Mitigation strategies for this vulnerability primarily involve applying the official FreeBSD security patches that address the improper memory clearing issue in the kernel's kldstat implementation. System administrators should ensure all FreeBSD systems are updated to versions 11.1-STABLE, 11.1-RELEASE-p4, 11.0-RELEASE-p15, 10.4-STABLE, 10.4-RELEASE-p3, or 10.3-RELEASE-p24, which contain the necessary fixes. Additionally, monitoring for unauthorized kldstat calls and implementing proper privilege controls on kernel module loading operations can help reduce the attack surface. The vulnerability highlights the importance of proper memory management practices in kernel code and demonstrates how seemingly minor implementation flaws can create significant security risks. Organizations should also consider implementing kernel memory protection mechanisms and regular security audits to identify similar issues in other kernel subsystems that might be vulnerable to similar information disclosure attacks.