CVE-2017-13711 in QEMU
Summary
by MITRE
Use-after-free vulnerability in the sofree function in slirp/socket.c in QEMU (aka Quick Emulator) allows attackers to cause a denial of service (QEMU instance crash) by leveraging failure to properly clear ifq_so from pending packets.
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Analysis
by VulDB Data Team • 12/27/2022
The vulnerability CVE-2017-13711 represents a critical use-after-free condition within QEMU's slirp networking stack implementation. This flaw exists in the sofree function located in slirp/socket.c, where the software fails to properly clear the ifq_so field when handling pending network packets. The issue stems from improper memory management practices that leave dangling pointers in the network packet queue structure, creating a scenario where freed memory regions may still be referenced by subsequent operations. Such memory corruption vulnerabilities are particularly dangerous in virtualization environments where QEMU serves as a foundational component for emulating hardware platforms and managing network communications between virtual machines and host systems.
The technical exploitation of this vulnerability occurs when QEMU processes network packets through its slirp networking subsystem, which is commonly used for providing network connectivity to virtual machines in various QEMU configurations. When the sofree function executes, it attempts to free network socket resources but does not adequately clear the ifq_so reference field that maintains pointers to pending packets in the queue. This incomplete cleanup allows attackers to manipulate the network packet flow in a way that causes the QEMU process to access freed memory locations, leading to unpredictable behavior and eventual process termination. The vulnerability specifically targets the packet queue management mechanism that handles network traffic between virtual machines and external networks, making it particularly impactful for virtualized environments where network connectivity is essential.
The operational impact of CVE-2017-13711 extends beyond simple denial of service to potentially compromise the stability and availability of virtualized environments. When exploited successfully, this vulnerability can cause complete QEMU instance crashes, forcing virtual machine restarts and disrupting services that depend on these virtualized platforms. System administrators managing virtualization infrastructures may experience unexpected downtime, especially in production environments where QEMU is used for hosting critical applications or services. The vulnerability's exploitation does not require elevated privileges within the guest operating system, making it particularly dangerous as attackers can leverage it from within compromised virtual machines or through network-based attacks against the virtualization layer. This characteristic aligns with attack patterns documented in the MITRE ATT&CK framework under the 'Execution' and 'Persistence' domains, where adversaries exploit software vulnerabilities to gain control over system resources.
Mitigation strategies for CVE-2017-13711 primarily focus on applying the official QEMU patches released by the project maintainers, which address the improper memory cleanup in the sofree function. System administrators should prioritize updating their QEMU installations to versions containing the fix, typically QEMU 2.10.0 or later, which properly clears the ifq_so field during socket resource deallocation. Additionally, implementing network segmentation and access controls can reduce the attack surface by limiting network access to QEMU instances and virtual machines. Monitoring for unusual network packet processing behavior or QEMU process crashes can help detect exploitation attempts, while maintaining up-to-date virtualization security policies ensures comprehensive protection against similar vulnerabilities. The vulnerability demonstrates the importance of proper memory management in network stack implementations and aligns with CWE-416, which catalogs use-after-free errors as a critical class of memory safety vulnerabilities that can lead to arbitrary code execution or system instability.