CVE-2016-9846 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator) built with the Virtio GPU Device emulator support is vulnerable to a memory leakage issue. It could occur while updating the cursor data in update_cursor_data_virgl. A guest user/process could use this flaw to leak host memory bytes, resulting in DoS for a host.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 07/22/2019
The vulnerability CVE-2016-9846 represents a critical memory management flaw within QEMU's Virtio GPU Device emulator implementation. This issue manifests specifically within the update_cursor_data_virgl function where improper memory handling leads to information disclosure and denial of service conditions. The vulnerability affects QEMU installations that are compiled with Virtio GPU Device emulator support, making it particularly relevant to virtualization environments that utilize GPU acceleration features. The flaw stems from inadequate bounds checking and memory allocation practices during cursor data updates, creating a pathway for malicious guest users to access host memory contents.
The technical exploitation of this vulnerability occurs through the cursor data update mechanism within the Virtio GPU emulation layer. When a guest process attempts to update cursor information, the update_cursor_data_virgl function fails to properly validate memory boundaries or allocate sufficient resources, leading to memory leakage. This memory leakage allows a guest user to read host memory contents byte by byte, potentially exposing sensitive information stored in memory. The vulnerability is classified under CWE-125 as an out-of-bounds read, which is a common pattern in memory safety issues. Attackers can leverage this flaw to perform reconnaissance on the host system, potentially extracting kernel memory, cryptographic keys, or other confidential data. The DoS aspect of this vulnerability occurs when the memory leakage consumes excessive host resources, leading to system instability or complete system hangs.
The operational impact of CVE-2016-9846 extends beyond simple information disclosure to encompass broader system security and availability concerns. Virtualization environments utilizing QEMU with Virtio GPU support become vulnerable to attacks that can compromise both data confidentiality and system availability. This vulnerability particularly affects cloud computing platforms, virtual desktop infrastructures, and any environment where guest operating systems have access to GPU emulation features. The attack vector requires only guest-level privileges, making it especially dangerous as it can be exploited by unprivileged users within virtual machines. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, and T1068 for exploit for privilege escalation, as it provides a foundation for further attacks. The vulnerability's impact is amplified in multi-tenant environments where guest isolation is critical for security.
Mitigation strategies for CVE-2016-9846 primarily involve immediate software updates and configuration changes. The most effective solution is to upgrade QEMU to versions that address the memory handling issues in the update_cursor_data_virgl function. System administrators should also consider disabling Virtio GPU Device emulator support when it is not required for virtual machine operations. Network segmentation and access controls can help limit the potential impact of exploitation, though these measures do not address the core vulnerability. Monitoring for unusual memory access patterns or excessive resource consumption can help detect exploitation attempts. The vulnerability highlights the importance of proper input validation and memory management in virtualization software, emphasizing the need for thorough security testing of emulator components. Organizations should also implement regular vulnerability assessments to identify similar memory safety issues in other virtualization components, as this type of flaw often indicates broader architectural weaknesses in memory management practices.