CVE-2017-5926 in AMD
Summary
by MITRE
Page table walks conducted by the MMU during virtual to physical address translation leave a trace in the last level cache of modern AMD processors. By performing a side-channel attack on the MMU operations, it is possible to leak data and code pointers from JavaScript, breaking ASLR.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability identified as CVE-2017-5926 represents a sophisticated side-channel attack targeting the memory management unit operations on modern AMD processors. This flaw exploits the inherent architectural behavior of the memory subsystem during virtual to physical address translation processes, specifically during page table walks that occur when the MMU translates virtual addresses to physical addresses. The vulnerability arises from the fact that these MMU operations leave residual traces in the last level cache, creating exploitable information leakage channels that can be harvested by malicious actors.
The technical implementation of this vulnerability leverages cache timing attacks to extract information about memory access patterns that should normally remain hidden from user-space applications. During normal operation, when the MMU performs page table walks to resolve virtual addresses, it accesses specific memory locations that are cached in the processor's last level cache. The attack exploits the timing variations in cache access patterns to infer information about the memory layout, particularly targeting data and code pointers that are critical for bypassing security mechanisms like Address Space Layout Randomization. This cache-based information leakage occurs at the hardware level and operates independently of traditional software-based security controls.
The operational impact of CVE-2017-5926 is particularly severe in web browser environments where JavaScript execution can be leveraged to perform the necessary cache probing operations. The vulnerability enables attackers to break ASLR protections that are fundamental to modern operating system security architectures, allowing for more sophisticated exploitation techniques including return-oriented programming and other advanced attack vectors. The attack can be executed from unprivileged JavaScript contexts, making it particularly dangerous in browser-based environments where sandboxing mechanisms are supposed to prevent such information leakage. This vulnerability directly relates to CWE-203: Information Exposure Through Implementation Flaws and aligns with ATT&CK technique T1059.007: Command and Scripting Interpreter: JavaScript, demonstrating how hardware-level flaws can be exploited through software-based attack vectors.
Mitigation strategies for CVE-2017-5926 require both architectural and software-level interventions to address the root cause of the cache-based information leakage. Processor vendors implemented microcode updates to modify the MMU behavior during page table walks, preventing the creation of exploitable cache traces. Operating system vendors developed kernel-level protections including memory access randomization techniques and enhanced cache management policies to reduce the effectiveness of such side-channel attacks. Browser vendors implemented additional security measures including JavaScript sandboxing enhancements and memory access control improvements. The vulnerability highlights the importance of considering side-channel attack vectors during security design phases and demonstrates how seemingly benign hardware behaviors can create exploitable security weaknesses. Organizations should maintain updated firmware and operating system patches while implementing additional security monitoring to detect potential exploitation attempts. This vulnerability serves as a critical reminder of the complex interplay between hardware architecture and software security, emphasizing the need for comprehensive security approaches that consider all layers of the computing stack.