CVE-2018-12617 in qemu-ga
Summary
by MITRE
qmp_guest_file_read in qga/commands-posix.c and qga/commands-win32.c in qemu-ga (aka QEMU Guest Agent) in QEMU 2.12.50 has an integer overflow causing a g_malloc0() call to trigger a segmentation fault when trying to allocate a large memory chunk. The vulnerability can be exploited by sending a crafted QMP command (including guest-file-read with a large count value) to the agent via the listening socket.
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Analysis
by VulDB Data Team • 12/01/2024
The vulnerability identified as CVE-2018-12617 represents a critical integer overflow flaw within the QEMU Guest Agent implementation that affects QEMU version 2.12.50 and potentially other versions in the affected release cycle. This vulnerability exists in the qmp_guest_file_read function which is responsible for handling file read operations from guest operating systems through the QEMU Guest Agent interface. The flaw manifests in both POSIX and Windows implementations of the guest agent commands, indicating a cross-platform vulnerability that could be exploited across different guest environments. The QEMU Guest Agent serves as a critical component for facilitating communication between the host and guest operating systems, enabling features such as file operations, guest information retrieval, and system management functions. When a malicious actor sends a crafted QMP command containing a large count parameter to the guest agent via its listening socket, the integer overflow condition triggers a memory allocation failure that ultimately results in a segmentation fault and potential system crash.
The technical root cause of this vulnerability stems from improper input validation and integer overflow handling within the memory allocation logic of the guest agent's file reading functionality. Specifically, when processing a guest-file-read command, the qmp_guest_file_read function fails to properly validate the count parameter that specifies how many bytes to read from a file. The integer overflow occurs during the calculation of memory requirements for the g_malloc0() allocation call, where an excessively large count value causes the resulting memory request to exceed the maximum allocatable size or wrap around to a small value, creating a situation where the guest agent attempts to allocate an impossibly large memory chunk. This memory allocation failure directly results in a segmentation fault as the system cannot fulfill the invalid memory request, causing the QEMU Guest Agent process to terminate unexpectedly. The vulnerability is classified as a CWE-190 Integer Overflow or Wraparound, which is a well-documented weakness in software security that occurs when an integer value exceeds its maximum representable value, leading to unexpected behavior in subsequent operations.
The operational impact of CVE-2018-12617 extends beyond simple service disruption to potentially enable more sophisticated attack vectors depending on the execution environment. In virtualized environments, this vulnerability could allow an attacker with access to the guest agent's communication channel to cause denial of service conditions that might disrupt guest operating system functionality or compromise the stability of the entire virtual machine. The vulnerability is particularly concerning because it operates at the guest agent level, meaning that exploitation requires only access to the QMP interface rather than deeper system privileges. The segmentation fault triggered by this vulnerability could potentially be leveraged to cause cascading failures in virtualized environments where guest agent stability is critical for proper VM management operations. Additionally, the attack surface is broadened by the fact that this vulnerability affects both POSIX and Windows implementations, making it applicable across diverse guest operating systems within the same virtualized infrastructure. The ATT&CK framework would categorize this vulnerability under T1499.004 Network Denial of Service and potentially T1059 Command and Scripting Interpreter if the attacker can escalate privileges through other means.
Mitigation strategies for CVE-2018-12617 should focus on both immediate patching and operational security measures to protect against exploitation. The primary and most effective mitigation is to upgrade to a patched version of QEMU that addresses the integer overflow in the guest agent's memory allocation logic, specifically versions that have been released with fixes for this particular vulnerability. Organizations should also implement network segmentation and access controls to limit exposure of the QEMU Guest Agent's listening socket to only trusted entities. Input validation and parameter sanitization should be enforced at the QMP command level to prevent malicious count values from reaching the vulnerable code path. Additionally, monitoring for unusual memory allocation patterns or segmentation fault occurrences in QEMU Guest Agent processes can help detect potential exploitation attempts. The vulnerability highlights the importance of robust input validation and memory management practices in guest agent implementations, as these components often serve as attack vectors in virtualized environments where they may be exposed to untrusted inputs from guest operating systems. Security teams should also consider implementing automated vulnerability scanning that can detect and alert on the presence of unpatched QEMU versions within their infrastructure, particularly those that are known to be vulnerable to this specific integer overflow condition.