CVE-2017-7718 in QEMU
Summary
by MITRE
hw/display/cirrus_vga_rop.h in QEMU (aka Quick Emulator) allow local guest OS privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) via vectors related to copying VGA data via the cirrus_bitblt_rop_fwd_transp_ and cirrus_bitblt_rop_fwd_ functions.
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Analysis
by VulDB Data Team • 12/01/2022
The vulnerability identified as CVE-2017-7718 resides within the QEMU virtual machine emulator's Cirrus VGA graphics acceleration implementation, specifically in the hw/display/cirrus_vga_rop.h file. This flaw affects the virtualization environment by permitting local guest operating system users with privileged access to execute malicious operations that result in denial of service conditions. The vulnerability manifests when processing VGA data copying operations through the cirrus_bitblt_rop_fwd_transp_ and cirrus_bitblt_rop_fwd_ functions, which are part of the Cirrus Logic CLGD 5446 graphics controller emulation that QEMU implements for virtualized environments.
The technical root cause of this vulnerability stems from inadequate bounds checking within the graphics rendering functions that handle bitblt (bit block transfer) operations. When guest operating systems execute graphics operations that involve these specific functions, the code fails to properly validate input parameters and memory access boundaries before performing data copying operations. This absence of proper input validation creates opportunities for out-of-bounds memory reads that can corrupt memory structures or cause the QEMU process to crash. The flaw represents a classic buffer over-read condition where the graphics processing code accesses memory locations beyond the allocated buffer boundaries, leading to unpredictable behavior and system instability.
The operational impact of this vulnerability extends beyond simple denial of service, as it can compromise the entire virtualized environment. Local guest users with sufficient privileges can exploit this weakness to cause QEMU processes to terminate unexpectedly, effectively disrupting virtual machine operations and potentially leading to data loss or service interruptions. The vulnerability is particularly concerning in multi-tenant virtualization environments where guest users might attempt to exploit this flaw to affect other virtual machines running on the same host system. This type of vulnerability can be leveraged to create persistent denial of service conditions that degrade overall system performance and availability.
Mitigation strategies for CVE-2017-7718 should focus on both immediate patching and operational hardening measures. The primary solution involves applying the official QEMU patch that implements proper bounds checking within the affected graphics functions, ensuring that all input parameters are validated before memory operations are performed. Organizations should also consider implementing virtual machine isolation measures and monitoring for unusual graphics processing patterns that might indicate exploitation attempts. From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and can be categorized under ATT&CK technique T1499.001 for network denial of service attacks. System administrators should also consider disabling unnecessary graphics acceleration features when they are not required for virtual machine operations, as this reduces the attack surface for such vulnerabilities.