CVE-2016-9104 in QEMU
Summary
by MITRE
Multiple integer overflows in the (1) v9fs_xattr_read and (2) v9fs_xattr_write functions in hw/9pfs/9p.c in QEMU (aka Quick Emulator) allow local guest OS administrators to cause a denial of service (QEMU process crash) via a crafted offset, which triggers an out-of-bounds access.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability CVE-2016-9104 represents a critical integer overflow issue affecting QEMU's 9p file system implementation, specifically within the v9fs_xattr_read and v9fs_xattr_write functions located in hw/9pfs/9p.c. This flaw arises from insufficient input validation when processing extended attributes in the 9p protocol implementation, creating a scenario where maliciously crafted offset values can trigger arithmetic overflow conditions. The vulnerability specifically impacts local guest OS administrators who possess administrative privileges within the emulated environment, enabling them to exploit this weakness for denial of service attacks against the QEMU process. The integer overflow occurs when the system attempts to calculate memory offsets for attribute data handling, where the overflowed values result in out-of-bounds memory access patterns that ultimately crash the QEMU emulator process.
The technical nature of this vulnerability aligns with CWE-190, which categorizes integer overflow conditions, and demonstrates how improper integer handling in system components can lead to memory corruption and process termination. When a guest administrator provides a crafted offset value that exceeds the maximum representable integer value for the system's data types, the subsequent arithmetic operations produce overflowed results that are then used as memory access offsets. This creates a direct path to memory corruption where the QEMU process attempts to access memory locations outside of its allocated address space, resulting in segmentation faults and process crashes. The 9p protocol implementation fails to validate that the calculated offsets remain within acceptable bounds for the attribute data structures, allowing attackers to manipulate the system's memory access patterns through carefully constructed input parameters.
The operational impact of CVE-2016-9104 extends beyond simple denial of service, as it represents a potential vector for more sophisticated attacks within virtualized environments where QEMU serves as the underlying emulation platform. In cloud computing and virtualization deployments, this vulnerability could be exploited to disrupt services running on virtual machines, potentially affecting multiple tenants in multi-tenant environments. The vulnerability affects QEMU versions prior to 2.7.0, making it particularly concerning for systems that have not been updated to receive the corresponding security patches. Attackers with local administrative access within guest operating systems can leverage this flaw to cause persistent service disruptions, making it a significant concern for organizations relying on virtualization technologies. The impact is particularly severe in enterprise environments where virtual machines host critical applications and services, as the QEMU process crash could lead to complete virtual machine shutdowns.
Mitigation strategies for CVE-2016-9104 primarily involve immediate patching of QEMU installations to versions 2.7.0 or later, which contain the necessary fixes for the integer overflow conditions in the 9p file system implementation. Organizations should also implement network segmentation and access controls to limit local administrative privileges within guest operating systems, reducing the attack surface for this particular vulnerability. Additionally, monitoring systems should be configured to detect unusual patterns of QEMU process crashes or memory access violations that might indicate exploitation attempts. The fix implemented by QEMU developers addresses the root cause by introducing proper bounds checking and integer overflow validation in the affected functions, ensuring that calculated offsets remain within valid memory access ranges before being used for attribute data operations. This remediation aligns with ATT&CK technique T1499.001, which covers network denial of service attacks, and demonstrates the importance of input validation in preventing memory corruption vulnerabilities in virtualization platforms. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across their virtualization infrastructure, particularly in environments where multiple QEMU instances are deployed.