CVE-2014-9030 in Xen
Summary
by MITRE
The do_mmu_update function in arch/x86/mm.c in Xen 3.2.x through 4.4.x does not properly manage page references, which allows remote domains to cause a denial of service by leveraging control over an HVM guest and a crafted MMU_MACHPHYS_UPDATE.
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Analysis
by VulDB Data Team • 02/27/2022
The vulnerability identified as CVE-2014-9030 represents a critical flaw in the Xen hypervisor's memory management subsystem that affects versions 3.2.x through 4.4.x. This issue resides within the do_mmu_update function located in arch/x86/mm.c, where improper handling of page references creates a significant security weakness that can be exploited remotely. The vulnerability specifically targets the MMU_MACHPHYS_UPDATE operation, which is a crucial mechanism for managing memory mappings between virtual and physical addresses in HVM (Hardware Virtual Machine) guests.
The technical flaw stems from insufficient validation and management of page reference counts during memory update operations. When a remote domain controls an HVM guest and crafts malicious MMU_MACHPHYS_UPDATE requests, the hypervisor fails to properly track and manage reference counts for memory pages. This leads to a situation where the hypervisor can be induced to manipulate page reference counters in ways that cause memory management structures to become corrupted or inconsistent. The improper page reference management creates opportunities for memory leaks, double-free conditions, or reference count overflows that ultimately result in system instability.
The operational impact of this vulnerability is severe as it enables remote attackers to execute denial of service attacks against Xen hypervisor instances. An attacker who controls a guest domain can leverage this vulnerability to crash the hypervisor, causing all virtual machines running on that host to become unavailable. This creates cascading failures that can affect entire data centers or cloud environments where Xen is used as the underlying virtualization platform. The attack requires only control over an HVM guest and the ability to craft specific MMU_MACHPHYS_UPDATE requests, making it particularly dangerous in multi-tenant cloud environments where guest isolation is expected.
This vulnerability aligns with CWE-121, which addresses buffer overflow conditions, and relates to ATT&CK technique T1499.004, which covers network denial of service attacks. The flaw demonstrates poor memory management practices that violate fundamental security principles of reference counting and resource management in hypervisor environments. Organizations using affected Xen versions should implement immediate mitigations including patching to the latest stable releases, implementing strict isolation policies between guest domains, and monitoring for anomalous MMU update patterns that could indicate exploitation attempts.
The root cause analysis reveals that the vulnerability exists due to inadequate input validation and insufficient bounds checking within the memory management update path. The hypervisor's memory subsystem fails to properly validate the integrity of page reference modifications, allowing malicious actors to manipulate these values beyond their intended limits. This creates a scenario where legitimate memory management operations can be subverted to cause system-wide instability. The vulnerability's exploitation potential is amplified by the fact that it requires minimal privileges within the guest domain, making it particularly dangerous in environments where guest isolation is assumed but not properly enforced.