CVE-2018-7550 in QEMU
Summary
by MITRE
The load_multiboot function in hw/i386/multiboot.c in Quick Emulator (aka QEMU) allows local guest OS users to execute arbitrary code on the QEMU host via a mh_load_end_addr value greater than mh_bss_end_addr, which triggers an out-of-bounds read or write memory access.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2018-7550 resides within the Quick Emulator QEMU software, specifically in the load_multiboot function located in hw/i386/multiboot.c. This issue represents a critical security flaw that enables local guest operating system users to escalate their privileges and execute arbitrary code on the host system running QEMU. The vulnerability stems from inadequate input validation within the multiboot loading mechanism, which is commonly used for booting operating systems in virtualized environments. When a malicious guest operating system attempts to load a multiboot image with a specially crafted mh_load_end_addr parameter that exceeds the mh_bss_end_addr value, the system fails to properly validate these memory boundaries, leading to exploitable memory access patterns.
The technical implementation of this vulnerability involves a classic buffer overflow condition that manifests as out-of-bounds read or write memory access operations. The load_multiboot function processes multiboot-compliant boot images without sufficient boundary checking between memory load addresses and bss section end addresses. This allows an attacker within the guest environment to manipulate memory layout parameters in such a way that they can access memory regions beyond the intended boundaries. The flaw operates at the memory management level of the emulator, where guest memory addresses are translated and loaded into the host system's memory space, creating a potential attack surface for privilege escalation.
From an operational impact perspective, this vulnerability presents a severe threat to virtualized environments where multiple users or untrusted operating systems share the same QEMU host infrastructure. The local guest user can leverage this flaw to execute arbitrary code on the host system, potentially leading to complete system compromise. This type of vulnerability is particularly dangerous in cloud computing environments, containerized deployments, and multi-tenant virtualization setups where isolation between guests is critical. The attack vector requires only local access within the guest operating system, making it accessible to any user with guest privileges, and could be exploited to gain root access on the host system, undermining the fundamental security model of virtualization.
The vulnerability aligns with CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write categories, both of which are classified under the Common Weakness Enumeration system as critical memory safety issues. From the MITRE ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and execution of malicious code in host environments. The exploitability of CVE-2018-7550 demonstrates the importance of input validation and memory boundary checking in virtualization software, as the flaw essentially allows guest users to bypass the isolation mechanisms that separate guest and host memory spaces. Organizations utilizing QEMU for virtualization must consider the implications of this vulnerability for their security posture, particularly in environments where guest users may not be trusted.
Mitigation strategies for this vulnerability should include immediate patching of QEMU installations to address the specific memory boundary checking issue in the load_multiboot function. System administrators should also implement additional security controls such as restricting guest user privileges, monitoring for anomalous memory access patterns, and ensuring proper virtualization isolation mechanisms are in place. The fix typically involves adding proper validation checks between memory load addresses and bss section boundaries, preventing maliciously crafted multiboot images from triggering out-of-bounds memory operations. Organizations should also consider implementing network segmentation and access controls to limit potential exploitation of this vulnerability in multi-tenant environments. Regular security audits and vulnerability assessments of virtualization infrastructure are essential to identify and remediate similar memory safety issues that could potentially lead to host compromise.