CVE-2017-7262 in Ryzen
Summary
by MITRE
The AMD Ryzen processor with AGESA microcode through 2017-01-27 allows local users to cause a denial of service (system hang) via an application that makes a long series of FMA3 instructions, as demonstrated by the Flops test suite.
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Analysis
by VulDB Data Team • 09/14/2020
The vulnerability identified as CVE-2017-7262 affects AMD Ryzen processors that utilize AGESA microcode versions released through January 27, 2017, representing a critical denial of service flaw that can be exploited by local attackers. This vulnerability specifically targets the processor's handling of FMA3 (Fused Multiply-Add) instructions, which are part of the x86 instruction set architecture designed for high-performance floating-point computations. The flaw manifests when applications execute extended sequences of FMA3 operations, causing the system to become unresponsive or enter a permanent hang state.
The technical implementation of this vulnerability stems from improper handling within the processor's microcode execution engine, where the FMA3 instruction set fails to properly manage resource allocation and execution flow when subjected to prolonged instruction sequences. This issue falls under CWE-129, which addresses improper validation of array indices, as the microcode does not adequately validate or limit the execution patterns of FMA3 instructions. The vulnerability is particularly concerning because it operates at the processor level, making it difficult to detect and mitigate through traditional software-based approaches.
From an operational perspective, this vulnerability presents a significant risk to system stability and availability, as local users with access to the affected systems can trigger system hangs that require manual intervention or power cycling to resolve. The Flops test suite serves as a practical demonstration of this vulnerability, showcasing how sustained FMA3 instruction execution can overwhelm the processor's execution units and cause the system to become unresponsive. This type of attack can be particularly damaging in environments where system uptime is critical, such as enterprise servers, financial transaction systems, or industrial control systems.
The exploitation of CVE-2017-7262 aligns with ATT&CK technique T1499.004, which covers "Evasion: Windows: System Shutdown/Reboot," as the denial of service effect can be achieved without requiring elevated privileges, making it accessible to local users. Organizations should consider implementing microcode updates provided by AMD to address this vulnerability, as the fix involves modifications to the AGESA firmware that regulate how FMA3 instructions are processed. Additionally, system administrators should monitor for unusual patterns of FMA3 instruction execution and consider implementing process monitoring to detect potential exploitation attempts. The vulnerability highlights the importance of firmware security and the need for comprehensive testing of microcode updates before deployment, as it demonstrates how low-level processor components can introduce significant stability risks.