CVE-2017-1086 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, not all information in the struct ptrace_lwpinfo is relevant for the state of any thread, and the kernel does not fill the irrelevant bytes or short strings. Since the structure filled by the kernel is allocated on the kernel stack and copied to userspace, a leak of information of the kernel stack of the thread is possible from the debugger. As a result, some bytes from the kernel stack of the thread using ptrace (PT_LWPINFO) call can be observed in userspace.
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Analysis
by VulDB Data Team • 01/24/2021
This vulnerability exists in FreeBSD operating systems prior to specific stable and release versions, representing a classic information disclosure flaw that arises from improper kernel memory handling during ptrace system calls. The issue specifically affects the struct ptrace_lwpinfo structure which is used to provide information about threads during debugging operations. When a debugger invokes the ptrace PT_LWPINFO call, the kernel populates this structure with thread information but fails to properly initialize all fields, leaving some bytes uninitialized or containing residual data from previous kernel operations.
The technical implementation of this vulnerability stems from the kernel's approach to memory management during the ptrace operation. The struct ptrace_lwpinfo structure is allocated on the kernel stack and subsequently copied to userspace for the debugger to examine. However, not all fields within this structure contain meaningful data for every thread state, yet the kernel does not explicitly zero out or sanitize these unused portions. This oversight creates a scenario where sensitive kernel memory contents, including potentially confidential data from other kernel operations or stack contents from previous function calls, can be inadvertently exposed to user-space processes that are debugging or tracing threads.
The operational impact of this vulnerability extends beyond simple information leakage, as it provides attackers with potential access to kernel memory contents that could contain sensitive data, cryptographic keys, or other confidential information. This type of information disclosure can enable further exploitation attempts, including privilege escalation or targeted attacks against the operating system. The vulnerability is particularly concerning because it occurs during legitimate debugging operations, making it difficult to detect and potentially allowing attackers to use standard debugging tools to harvest kernel memory contents without raising suspicious alerts.
The flaw aligns with CWE-248, an information exposure vulnerability, and demonstrates how improper initialization of data structures can lead to memory leakage in kernel space. From an attack perspective, this vulnerability maps to techniques described in the ATT&CK framework under T1059 for execution through debugging tools and T1005 for data from local system. The vulnerability is particularly dangerous in environments where multiple applications or users have access to debugging capabilities, as it can be exploited by malicious actors to gather information about running kernel processes and their memory contents. This makes the vulnerability relevant to both local and potentially remote attack scenarios, depending on the system configuration and access controls in place.
The recommended mitigations include upgrading to the patched versions of FreeBSD mentioned in the vulnerability description, which properly initialize all fields within the ptrace_lwpinfo structure. System administrators should also implement strict access controls on debugging and ptrace capabilities, limiting who can invoke these operations. Additionally, monitoring for unusual ptrace activity and implementing kernel memory protection mechanisms can help detect and prevent exploitation attempts. Organizations should conduct thorough security assessments to identify systems running vulnerable FreeBSD versions and ensure timely patch deployment to prevent potential exploitation of this information disclosure vulnerability.