CVE-2017-1000372 in OpenBSD
Summary
by MITRE
A flaw exists in OpenBSD's implementation of the stack guard page that allows attackers to bypass it resulting in arbitrary code execution using setuid binaries such as /usr/bin/at. This affects OpenBSD 6.1 and possibly earlier versions.
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Analysis
by VulDB Data Team • 12/29/2020
The vulnerability identified as CVE-2017-1000372 represents a critical stack canary bypass in OpenBSD's memory protection mechanisms that fundamentally undermines the operating system's security model. This flaw specifically targets the implementation of stack guard pages within the OpenBSD kernel, which are designed to detect and prevent stack-based buffer overflow attacks by placing a protected page between the stack and other memory regions. The vulnerability exists in OpenBSD version 6.1 and potentially earlier releases, making it a widespread issue affecting a significant portion of the OpenBSD user base.
The technical implementation of this vulnerability stems from an improper handling of stack guard page permissions within the kernel's memory management subsystem. When setuid binaries execute, they typically operate with elevated privileges and are subject to additional security checks including stack canary protection. However, the flaw in OpenBSD's implementation allows attackers to manipulate memory mappings in such a way that the stack guard page becomes accessible, effectively neutralizing the protection mechanism. This occurs through a specific sequence of memory operations that exploit the kernel's memory management routines to alter page permissions and bypass the intended security boundaries.
The operational impact of this vulnerability is particularly severe given that it affects setuid binaries, which are critical system components that operate with elevated privileges. The most notable affected binary mentioned in the vulnerability description is /usr/bin/at, which is a command-line utility for scheduling tasks that runs with elevated privileges. Attackers can leverage this bypass to execute arbitrary code with the privileges of the setuid binary, potentially escalating their access to full system compromise. This vulnerability essentially provides a path for privilege escalation attacks that can be executed by unprivileged users, making it a significant threat to system integrity.
The security implications extend beyond simple privilege escalation, as this vulnerability aligns with several attack patterns documented in the ATT&CK framework under privilege escalation techniques. Specifically, it relates to techniques involving exploitation of kernel vulnerabilities and memory corruption, which are commonly used in advanced persistent threat campaigns. From a CWE perspective, this vulnerability maps to CWE-129, which covers improper validation of array indices, and CWE-248, which addresses exposure of an exception to external entities. The flaw essentially creates an exception in the kernel's memory protection that allows unauthorized access to protected memory regions, making it a critical component in the exploitation chain for various advanced attacks.
Mitigation strategies for this vulnerability require immediate system updates and patches from OpenBSD maintainers, as the flaw exists at the kernel level and cannot be addressed through user-space workarounds. System administrators should prioritize applying the official OpenBSD security patches that correct the stack guard page implementation and restore proper memory protection boundaries. Additional defensive measures include implementing mandatory access controls such as OpenBSD's pledge and unveil system calls to limit the attack surface of vulnerable setuid binaries. Network segmentation and monitoring for suspicious execution patterns of setuid binaries can also provide additional layers of defense. Organizations should also consider implementing runtime application protection mechanisms and regular security auditing of setuid binaries to detect potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper kernel memory management and the need for continuous security validation of core operating system components.