CVE-2017-5927 in ARM
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 ARM 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 described in CVE-2017-5927 represents a sophisticated side-channel attack targeting the memory management unit operations within modern ARM processors. This flaw exploits the inherent architectural characteristics of how virtual to physical address translation occurs, specifically during page table walks that traverse the memory hierarchy. The vulnerability stems from the fact that during these critical MMU operations, cache lines containing page table entries are accessed and cached, creating observable timing variations that can be exploited by malicious code running in the same execution environment. The attack leverages the fact that different memory locations have distinct cache access patterns, allowing an attacker to infer information about the memory layout through careful observation of cache behavior.
The technical implementation of this vulnerability involves exploiting the cache coherency mechanisms present in ARM processors, particularly focusing on the last level cache where page table entries are stored during translation operations. When JavaScript code executes and accesses memory, the MMU performs page table walks to resolve virtual addresses to physical locations, and these operations leave characteristic cache access patterns that can be monitored and analyzed. The attacker can observe these patterns through timing measurements or cache state monitoring techniques, which reveal information about the memory mapping structure. This particularly affects address space layout randomization mechanisms since the cache-based side-channel can reveal the locations of code segments and data structures that would normally be protected by randomization.
The operational impact of CVE-2017-5927 is significant within the context of web browser security and sandboxed environments where JavaScript execution occurs. The vulnerability effectively undermines the security boundary between user-space code and system-level memory management, allowing attackers to extract pointers and memory addresses that would normally remain hidden. This breaking of ASLR creates a pathway for more sophisticated attacks that might otherwise be blocked by memory layout randomization, potentially enabling privilege escalation or information disclosure attacks. The vulnerability is particularly concerning in mobile and embedded environments where ARM processors are prevalent, as it demonstrates how architectural features designed for performance can inadvertently create security weaknesses. This type of attack aligns with the broader category of cache-based side-channel attacks that have been increasingly documented in the security literature, and it reflects the ongoing challenges in securing modern processor architectures against sophisticated exploitation techniques.
Mitigation strategies for this vulnerability typically involve implementing software-level protections such as cache flushing operations during critical memory management operations, or modifying the operating system kernel to prevent predictable cache access patterns during page table walks. The approach often involves introducing randomization or additional overhead in memory management operations to eliminate the observable timing differences that enable the attack. System administrators and security professionals should consider updating to patched versions of affected operating systems and browser implementations, while also implementing monitoring solutions to detect potential exploitation attempts. This vulnerability demonstrates the importance of considering side-channel attack vectors during security design reviews, as it highlights how seemingly benign architectural features can create exploitable weaknesses. The attack pattern is consistent with techniques documented in various security frameworks and represents a specific instance of cache timing attacks that fall under the broader category of information leakage through side channels. Organizations should also consider implementing additional security controls such as memory access monitoring and anomaly detection systems to identify potential exploitation attempts.