CVE-2014-1891 in Xen
Summary
by MITRE
Multiple integer overflows in the (1) FLASK_GETBOOL, (2) FLASK_SETBOOL, (3) FLASK_USER, and (4) FLASK_CONTEXT_TO_SID suboperations in the flask hypercall in Xen 4.3.x, 4.2.x, 4.1.x, 3.2.x, and earlier, when XSM is enabled, allow local users to cause a denial of service (processor fault) via unspecified vectors, a different vulnerability than CVE-2014-1892, CVE-2014-1893, and CVE-2014-1894.
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Analysis
by VulDB Data Team • 05/09/2026
The vulnerability identified as CVE-2014-1891 represents a critical security flaw affecting the Xen hypervisor version 4.3.x, 4.2.x, 4.1.x, and 3.2.x series when the eXtensible Security Module (XSM) is enabled. This issue manifests through integer overflow conditions within four specific suboperations of the flask hypercall interface: FLASK_GETBOOL, FLASK_SETBOOL, FLASK_USER, and FLASK_CONTEXT_TO_SID. These suboperations form part of Xen's mandatory access control mechanisms that enforce security policies for virtual machine isolation. The vulnerability arises from insufficient input validation and arithmetic overflow handling in the kernel-level hypercall interface that manages security context transitions between virtual machines and the host system.
The technical exploitation of this vulnerability occurs when local users within a virtual machine can manipulate parameters passed to these flask hypercall suboperations. Integer overflows in kernel space can result in unpredictable behavior including memory corruption, privilege escalation, or system crashes that manifest as processor faults. The specific nature of these overflows suggests that the hypervisor fails to properly validate the size or range of input parameters before performing arithmetic operations, leading to situations where computed values exceed the maximum representable integer values for the target data types. This class of vulnerability falls under the common weakness enumeration CWE-190, which specifically addresses integer overflow conditions in software systems. The flaw is particularly dangerous because it operates within the hypervisor's security module, potentially allowing attackers to undermine the fundamental isolation properties that virtualization environments rely upon for security.
The operational impact of CVE-2014-1891 extends beyond simple denial of service scenarios to potentially compromise the entire virtualization infrastructure. When a processor fault occurs due to integer overflow in the hypervisor's security subsystem, it can cause complete system crashes or allow unauthorized access to other virtual machines running on the same physical host. This vulnerability directly threatens the security model of Xen hypervisors, as it enables attackers to bypass mandatory access controls that are designed to prevent unauthorized interactions between virtual machines. The attack vector involves local users within a compromised guest operating system who can leverage these integer overflows to trigger system instability. According to ATT&CK framework, this vulnerability maps to techniques involving privilege escalation and denial of service, specifically targeting the hypervisor layer where attackers can manipulate system calls to compromise host integrity.
Mitigation strategies for this vulnerability require immediate patching of affected Xen versions to address the integer overflow conditions in the flask hypercall interface. System administrators should prioritize upgrading to patched versions of Xen hypervisor, as the vulnerability affects multiple major release series and represents a fundamental flaw in the security module implementation. Additional defensive measures include implementing strict input validation at the hypervisor level, enabling kernel address space layout randomization, and monitoring for anomalous hypercall patterns that might indicate exploitation attempts. Organizations should also consider isolating critical workloads on patched systems and implementing network segmentation to limit the potential impact of successful exploitation. The vulnerability demonstrates the importance of rigorous input validation and integer overflow protection in kernel-space code, particularly within security-critical components that handle inter-vm communications and access control decisions.