CVE-2017-11434 in QEMU
Summary
by MITRE
The dhcp_decode function in slirp/bootp.c in QEMU (aka Quick Emulator) allows local guest OS users to cause a denial of service (out-of-bounds read and QEMU process crash) via a crafted DHCP options string.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-11434 resides within the QEMU virtualization platform's slirp networking component, specifically in the dhcp_decode function located in slirp/bootp.c. This issue represents a critical security flaw that affects the hypervisor's ability to properly validate DHCP option strings received from guest operating systems. The vulnerability manifests when a malicious guest OS user crafts a specially formatted DHCP options string that triggers improper memory handling within the QEMU process, leading to an out-of-bounds read condition that ultimately results in a complete system crash.
The technical implementation of this vulnerability stems from insufficient input validation within the DHCP decoding routine. When QEMU processes DHCP packets, the dhcp_decode function fails to properly bounds-check the incoming DHCP options data before attempting to parse and interpret the contained information. This lack of proper validation allows an attacker within the guest OS to craft a DHCP option string that exceeds the expected buffer boundaries, causing the function to read memory locations outside of its allocated buffer space. The vulnerability maps directly to CWE-129, which describes improper validation of array indices, and CWE-787, which covers out-of-bounds write operations that can lead to memory corruption.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides a potential attack vector for more sophisticated exploitation attempts. A local guest OS user can leverage this vulnerability to crash the QEMU process, effectively causing a denial of service against the virtual machine hosting the compromised guest. This can result in complete system unavailability, data loss, and potential compromise of the host system if the guest is running privileged processes. The attack requires minimal privileges since it operates from within the guest OS environment, making it particularly concerning for multi-tenant virtualization environments where guest isolation is paramount.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059.001, which covers command and script injection, as it enables an attacker to execute code within the guest OS that can then be leveraged to cause system instability. The vulnerability also relates to T1499.004, which covers network denial of service attacks, as the crafted DHCP options can be used to disrupt network connectivity within the virtualized environment. Organizations using QEMU for virtualization must consider this vulnerability as a critical threat that can undermine the reliability and security of their virtualized infrastructure.
Mitigation strategies for CVE-2017-11434 should prioritize immediate patching of affected QEMU versions, with administrators ensuring that all virtualization environments are updated to versions that contain the appropriate input validation fixes. Network administrators should also implement additional monitoring and intrusion detection systems to identify anomalous DHCP traffic patterns that might indicate exploitation attempts. The fix typically involves implementing proper bounds checking within the dhcp_decode function to validate DHCP option string lengths before processing, preventing the out-of-bounds memory access that leads to the crash condition. Organizations should also consider implementing network segmentation and access controls to limit guest OS privileges and reduce the attack surface available to potential attackers.