CVE-2017-5987 in QEMU
Summary
by MITRE
The sdhci_sdma_transfer_multi_blocks function in hw/sd/sdhci.c in QEMU (aka Quick Emulator) allows local OS guest privileged users to cause a denial of service (infinite loop and QEMU process crash) via vectors involving the transfer mode register during multi block transfer.
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Analysis
by VulDB Data Team • 11/14/2022
The vulnerability identified as CVE-2017-5987 resides within the QEMU virtual machine emulator's SDHCI (Secure Digital Host Controller Interface) implementation, specifically in the sdhci_sdma_transfer_multi_blocks function located in hw/sd/sdhci.c. This flaw represents a critical security issue that affects virtualized environments where guest operating systems can potentially exploit the emulator's handling of multi-block data transfers. The vulnerability manifests when the transfer mode register is improperly configured during multi-block transfer operations, creating a condition that can lead to system instability and complete service disruption.
The technical root cause of this vulnerability stems from inadequate input validation and boundary checking within the SDHCI controller emulation layer. When a guest operating system attempts to perform multi-block transfers using the SDMA (SD Memory Access) mode, the function fails to properly validate the transfer mode register values, particularly those related to the transfer direction and block count parameters. This validation failure creates an execution path where the emulator enters an infinite loop condition, continuously processing transfer requests without proper termination conditions. The flaw is classified under CWE-697, which deals with incorrect comparison conditions that can lead to unintended program behavior and system instability.
From an operational perspective, this vulnerability poses significant risks to virtualized environments where QEMU serves as the primary hypervisor platform. Local privileged users within the guest operating system can exploit this flaw to cause denial of service conditions that affect the entire virtual machine instance. The infinite loop condition results in complete QEMU process crashes, effectively terminating the virtual machine and disrupting all running services within that environment. This type of vulnerability directly impacts availability as defined in the CIA triad, making it particularly dangerous in production environments where system uptime is critical. The attack vector requires only local access within the guest system, making it accessible to any user with sufficient privileges to interact with the SDHCI controller, which is common in many operating system configurations.
The implications of this vulnerability extend beyond simple service disruption, as it can be leveraged as a stepping stone for more sophisticated attacks within virtualized environments. Security researchers have documented similar patterns in SDHCI controller implementations where improper handling of transfer mode registers can lead to privilege escalation or information disclosure. The ATT&CK framework categorizes this type of vulnerability under T1499.004, which covers network denial of service, though in this case the impact occurs within the hypervisor layer rather than the network stack. Organizations running QEMU-based virtualization platforms must consider this vulnerability as part of their broader security posture, particularly in environments where guest operating systems may have elevated privileges or where multiple tenants share the same virtualization infrastructure.
Mitigation strategies for CVE-2017-5987 should focus on both immediate patching and operational hardening measures. The primary solution involves applying the official QEMU patches that address the improper validation of transfer mode register values in the sdhci_sdma_transfer_multi_blocks function. Organizations should also implement network segmentation and privilege restrictions within guest operating systems to limit the potential impact of local privilege escalation. Additionally, monitoring systems should be configured to detect unusual CPU utilization patterns or process crashes that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation in virtualization components, as recommended by the OWASP Top 10 security framework, particularly in areas related to resource management and access control. Regular security assessments of virtualization platforms should include thorough testing of emulated hardware controllers to identify similar validation flaws that could lead to system instability or privilege escalation.