CVE-2017-1085 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.2-RELEASE, an application which calls setrlimit() to increase RLIMIT_STACK may turn a read-only memory region below the stack into a read-write region. A specially crafted executable could be exploited to execute arbitrary code in the user context.
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Analysis
by VulDB Data Team • 07/11/2024
This vulnerability exists in FreeBSD operating systems prior to version 11.2-RELEASE and represents a critical memory management flaw that undermines the kernel's stack protection mechanisms. The issue arises from how the setrlimit() system call handles memory region permissions when increasing the stack limit, creating a potential pathway for privilege escalation and code execution. The vulnerability specifically affects applications that attempt to expand their stack resource limits beyond the default boundaries, exposing a fundamental flaw in the kernel's memory protection architecture. According to CWE-121, this represents a stack-based buffer overflow condition where memory permissions are improperly managed, while the ATT&CK framework categorizes this under privilege escalation techniques through memory corruption vulnerabilities. The flaw allows an attacker to manipulate memory permissions in a way that transforms read-only memory segments into read-write regions, creating an exploitable condition.
The technical implementation of this vulnerability exploits the interaction between the kernel's memory management subsystem and user-space applications that attempt to modify resource limits. When an application calls setrlimit() to increase RLIMIT_STACK, the kernel processes this request and modifies memory region permissions accordingly. However, in affected FreeBSD versions, the kernel fails to properly validate or enforce memory permission boundaries, particularly concerning memory regions located below the stack pointer. This creates a scenario where memory pages that should remain read-only become writable, allowing malicious code to overwrite critical memory locations. The vulnerability leverages the fact that memory regions below the stack can be manipulated through improper permission handling during stack limit expansion. The flaw is particularly dangerous because it occurs within the user context, meaning that exploitation does not require kernel-level privileges, making it accessible to any application running on the system.
The operational impact of this vulnerability extends beyond simple code execution, as it fundamentally compromises the memory protection mechanisms that FreeBSD relies upon for system security. An attacker who successfully exploits this vulnerability can execute arbitrary code with the privileges of the compromised application, potentially leading to full system compromise if the application runs with elevated permissions. The vulnerability affects system stability by creating unpredictable memory states where read-only segments become writable, potentially causing system crashes or allowing further exploitation through chained vulnerabilities. The risk is amplified because the exploit can be triggered by any application that calls setrlimit(), making it difficult to detect and prevent through traditional application monitoring. This vulnerability directly impacts the integrity of the memory management subsystem, as it allows unauthorized modification of memory permissions that should remain protected.
Mitigation strategies for this vulnerability require immediate system updates to FreeBSD 11.2-RELEASE or later versions where the kernel memory management has been patched to properly enforce memory permission boundaries. System administrators should also implement strict monitoring of setrlimit() calls and resource limit modifications, particularly when these modifications involve stack size increases. The patch addresses the underlying kernel memory management flaw by ensuring that when RLIMIT_STACK is increased, memory regions below the stack are not inadvertently granted write permissions. Additional defensive measures include implementing mandatory access controls, using memory protection features such as stack canaries, and conducting regular security audits of applications that manipulate resource limits. Organizations should also consider implementing application whitelisting and runtime protection mechanisms that can detect and prevent suspicious memory permission changes. The vulnerability highlights the importance of maintaining up-to-date operating system versions and the critical need for proper memory management validation in kernel code, as specified in security standards requiring robust memory protection mechanisms.