CVE-2018-9056 in CPU
Summary
by MITRE
Systems with microprocessors utilizing speculative execution may allow unauthorized disclosure of information to an attacker with local user access via a side-channel attack on the directional branch predictor, as demonstrated by a pattern history table (PHT), aka BranchScope.
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Analysis
by VulDB Data Team • 01/17/2020
The vulnerability identified as CVE-2018-9056 represents a critical side-channel attack mechanism that exploits speculative execution behaviors in modern microprocessors. This flaw specifically targets the directional branch predictor component within processor architectures, leveraging the inherent speculative execution capabilities to potentially expose sensitive information. The vulnerability operates through what is known as BranchScope, a sophisticated attack vector that demonstrates how pattern history table entries can be manipulated to disclose confidential data. The attack requires local user access and exploits the fundamental design principles of modern processors that attempt to optimize performance by predicting branch outcomes before they are definitively resolved.
The technical implementation of this vulnerability stems from the processor's directional branch predictor architecture, which maintains a pattern history table to predict the direction of conditional branches. During speculative execution, processors may execute instructions based on predicted branch outcomes before the actual branch resolution occurs. The BranchScope attack specifically targets the pattern history table structure, where an attacker can manipulate the predictor's behavior to extract information about memory contents. This occurs because the processor's branch predictor maintains state information that can be indirectly observed through timing variations or cache behavior changes, allowing an attacker to reconstruct sensitive data that should remain confidential. The vulnerability is particularly concerning because it operates at the architectural level and affects processors from major manufacturers including intel, amd, and arm.
The operational impact of CVE-2018-9056 extends beyond simple information disclosure, representing a fundamental weakness in processor security design that can be exploited for privilege escalation and data exfiltration. Attackers with local access can potentially extract cryptographic keys, passwords, and other sensitive information from memory locations that are normally protected by operating system security mechanisms. The attack's effectiveness is amplified by the widespread adoption of speculative execution across modern processor architectures, making it a pervasive threat that affects numerous computing platforms. This vulnerability particularly impacts systems that rely on traditional security models where local users are assumed to be trusted, as the attack can bypass many conventional security boundaries. The implications are severe for enterprise environments where local access might be more prevalent than anticipated, and where sensitive data processing occurs on potentially vulnerable hardware.
Mitigation strategies for CVE-2018-9056 require a multi-layered approach that addresses both software and hardware vulnerabilities. System administrators should implement microcode updates provided by processor vendors to modify branch predictor behavior and reduce information leakage through side channels. Operating system patches and kernel modifications can help by implementing additional protections against speculative execution attacks, including the use of retpoline techniques and other mitigations that prevent the exploitation of branch prediction vulnerabilities. Memory access controls and privilege separation mechanisms should be enhanced to limit the potential impact of successful attacks, while monitoring systems should be deployed to detect anomalous behavior that might indicate exploitation attempts. Organizations must also consider architectural mitigations such as disabling speculative execution features where possible, though this approach may impact performance. The implementation of these mitigations should follow industry standards including those defined in the CWE catalog under category 200 for information exposure and the ATT&CK framework's techniques related to privilege escalation and credential access through hardware-level vulnerabilities.