CVE-2021-26348 in EPYC
Summary
by MITRE • 05/11/2022
Failure to flush the Translation Lookaside Buffer (TLB) of the I/O memory management unit (IOMMU) may lead an IO device to write to memory it should not be able to access, resulting in a potential loss of integrity.
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Analysis
by VulDB Data Team • 05/14/2022
The vulnerability identified as CVE-2021-26348 represents a critical flaw in memory management systems where the Translation Lookaside Buffer of the I/O Memory Management Unit fails to properly flush cached translations. This issue manifests when virtual to physical address mappings are not adequately invalidated during I/O operations, creating a persistent security weakness that can be exploited by malicious actors. The vulnerability affects systems that rely on IOMMU for memory protection, particularly those implementing virtualization technologies or hardware-assisted memory management. From a technical perspective, this represents a failure in the memory management unit's ability to maintain consistent address translation tables, which directly violates fundamental security principles of memory isolation and access control.
The core technical flaw lies in the improper handling of TLB invalidation mechanisms within the IOMMU subsystem. When I/O devices perform memory operations, they rely on cached translations from the TLB to map virtual addresses to physical memory locations. The failure to flush these translations means that stale mappings can persist even when memory protections have been updated or changed. This creates a window of opportunity for unauthorized memory access where an I/O device could potentially write to memory regions it should not have access to, leading to data corruption, privilege escalation, or information disclosure. The vulnerability is particularly concerning because it operates at a low level within the hardware memory management system, making it difficult to detect and exploit through conventional software-based security measures.
The operational impact of CVE-2021-26348 extends beyond simple memory integrity violations to encompass broader system security implications. Attackers could potentially leverage this vulnerability to bypass memory protection mechanisms, escalate privileges, or gain access to sensitive data that should be isolated from untrusted I/O devices. In virtualized environments, this flaw could enable a guest operating system to access memory belonging to other guests or the host system, effectively breaking the isolation guarantees that virtualization platforms rely upon. The vulnerability affects systems using Intel VT-d and AMD-Vi IOMMU implementations, making it widespread across modern server and workstation platforms. According to CWE classification, this corresponds to CWE-1160: Improper Flushing of Translation Lookaside Buffer, which directly relates to the improper handling of memory management unit cache invalidation. The attack surface is further expanded by the fact that this vulnerability can be exploited through various I/O operations including DMA attacks, where malicious devices can manipulate memory through direct hardware access.
Mitigation strategies for CVE-2021-26348 require both firmware and software level interventions to ensure proper TLB flushing mechanisms are implemented. System administrators should prioritize updating firmware and kernel components that contain patches addressing the specific IOMMU TLB flushing behavior. The recommended approach includes enabling IOMMU with appropriate memory protection settings, ensuring that all I/O device drivers properly handle memory mappings, and implementing regular system updates to maintain current security patches. Organizations should also consider implementing runtime monitoring to detect anomalous I/O memory access patterns that could indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and defense evasion through hardware-level manipulation, specifically targeting the system's memory management infrastructure. The vulnerability demonstrates the critical importance of maintaining proper cache coherency and memory protection mechanisms, as highlighted in security best practices for hardware-assisted virtualization and memory management systems.