CVE-2016-6835 in QEMU
Summary
by MITRE
The vmxnet_tx_pkt_parse_headers function in hw/net/vmxnet_tx_pkt.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (buffer over-read) by leveraging failure to check IP header length.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6835 resides within the vmxnet_tx_pkt_parse_headers function in QEMU's network driver implementation, specifically in the hw/net/vmxnet_tx_pkt.c file. This flaw represents a classic buffer over-read condition that occurs when the virtual machine's network stack fails to properly validate the length of IP headers before processing them. The issue manifests when a local guest operating system administrator crafts malicious network packets with malformed IP header lengths, exploiting the absence of proper input validation in the virtualized network interface driver.
From a technical perspective, this vulnerability stems from inadequate bounds checking within the network packet processing pipeline of QEMU's vmxnet driver implementation. The function processes transmitted network packets from guest operating systems but does not verify that the IP header length field contains a valid value before proceeding with packet analysis. This allows an attacker to manipulate the IP header length field to point beyond the allocated buffer boundaries, resulting in a buffer over-read condition. The vulnerability is classified under CWE-129 as an insufficient input validation, specifically dealing with improper validation of input length parameters. The flaw represents a failure in the principle of defensive programming where input validation should occur before any processing of network data occurs.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially be exploited to crash the QEMU process or cause system instability. When a guest administrator sends malformed packets with excessive IP header lengths, the vmxnet driver attempts to read beyond the allocated memory space, leading to unpredictable behavior that can result in complete system crashes or hangs. This vulnerability affects virtualized environments where QEMU is used as the hypervisor, particularly impacting cloud computing platforms, virtual desktop infrastructures, and any system relying on QEMU for virtual machine operations. The local privilege escalation aspect means that even guests with limited administrative rights can potentially disrupt the host system's network functionality, making this a significant concern for multi-tenant virtualization environments.
Mitigation strategies for CVE-2016-6835 should focus on both immediate patching and operational security measures. The primary solution involves applying the official QEMU patch that implements proper IP header length validation before packet processing occurs. Organizations should also implement network segmentation and monitoring to detect anomalous packet patterns that might indicate exploitation attempts. From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.001 which involves network denial of service attacks. Additional defensive measures include implementing network intrusion detection systems that can identify malformed IP packets and configuring virtual machine network policies to limit guest administrative privileges where possible. The vulnerability demonstrates the importance of proper input validation in virtualized network components and highlights the need for comprehensive security testing of hypervisor network drivers.