CVE-2016-6888 in QEMU
Summary
by MITRE
Integer overflow in the net_tx_pkt_init function in hw/net/net_tx_pkt.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (QEMU process crash) via the maximum fragmentation count, which triggers an unchecked multiplication and NULL pointer dereference.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6888 represents a critical integer overflow condition within the QEMU virtualization environment that affects the network subsystem's packet handling mechanism. This flaw exists in the net_tx_pkt_init function located in the hw/net/net_tx_pkt.c source file, which is part of the QEMU emulator's hardware emulation layer. The vulnerability specifically manifests when processing network packets with maximum fragmentation counts, creating a scenario where unchecked arithmetic operations can lead to system instability and complete service disruption.
The technical exploitation of this vulnerability relies on an integer overflow occurring during multiplication operations within the network packet initialization process. When a guest operating system administrator manipulates the fragmentation count parameter beyond acceptable limits, the multiplication operation fails to properly validate the result, leading to an overflow condition that produces a value insufficient to allocate proper memory structures. This overflow condition subsequently results in a NULL pointer dereference, as the system attempts to access memory locations that were never properly initialized or allocated, causing the QEMU process to terminate abruptly and resulting in a denial of service condition.
From an operational perspective, this vulnerability presents a significant risk to virtualized environments where guest operating systems may have administrative privileges or where malicious actors can gain elevated access within the guest environment. The impact extends beyond simple service disruption as it can affect the entire virtualization infrastructure, potentially causing cascading failures across multiple virtual machines running on the same host. The vulnerability is particularly concerning in cloud computing environments where QEMU serves as the underlying hypervisor for numerous virtual instances, as a single compromised guest could potentially bring down the entire virtualization platform.
The vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and demonstrates the importance of proper input validation and arithmetic operation checking in security-critical systems. From an ATT&CK framework perspective, this vulnerability maps to the T1499 technique related to network denial of service, where adversaries can leverage system-level flaws to disrupt network services. The flaw also intersects with T1068, which covers privilege escalation through local system exploitation, as it allows local guest administrators to cause system-wide disruptions. Mitigation strategies should include immediate patching of QEMU installations to version 2.7.0 or later, which contains the necessary fixes for this integer overflow condition. Additionally, implementing network segmentation and access controls to limit guest administrative privileges can reduce the attack surface, while monitoring for unusual fragmentation patterns in network traffic can help detect potential exploitation attempts.