CVE-2015-6654 in Xen
Summary
by MITRE
The xenmem_add_to_physmap_one function in arch/arm/mm.c in Xen 4.5.x, 4.4.x, and earlier does not limit the number of printk console messages when reporting a failure to retrieve a reference on a foreign page, which allows remote domains to cause a denial of service by leveraging permissions to map the memory of a foreign guest.
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Analysis
by VulDB Data Team • 06/13/2022
The vulnerability identified as CVE-2015-6654 resides within the Xen hypervisor's memory management subsystem, specifically in the xenmem_add_to_physmap_one function located in arch/arm/mm.c. This flaw affects Xen versions 4.5.x, 4.4.x, and earlier releases, representing a significant security weakness that undermines the hypervisor's stability and integrity. The vulnerability manifests as an insufficient limitation of printk console messages during foreign page reference retrieval failures, creating a potential denial of service vector that can be exploited by malicious remote domains.
The technical flaw stems from the function's inadequate handling of error conditions when attempting to access foreign guest memory through the physical memory mapping mechanism. When a domain attempts to map memory from another guest and encounters a failure to retrieve a reference on a foreign page, the xenmem_add_to_physmap_one function generates an uncontrolled number of printk messages to the console. This behavior occurs without any rate limiting or message count restrictions, allowing an attacker to repeatedly trigger these error conditions and flood the system's console output.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it enables remote domains to consume system resources and potentially disrupt the normal operation of the hypervisor. Attackers can leverage their permissions to map foreign guest memory to repeatedly trigger the error condition, causing excessive console logging that may lead to system instability or complete denial of service. This vulnerability particularly affects systems where console output is directed to limited resources or where excessive logging could impact system performance.
The flaw aligns with CWE-770, which addresses the allocation of resources without proper limits, and demonstrates the importance of implementing proper resource management in hypervisor environments. From an ATT&CK perspective, this vulnerability maps to T1499.004, which covers the use of denial of service techniques through resource exhaustion, and T1068, which involves privilege escalation through improper access controls. The vulnerability represents a critical weakness in Xen's memory management architecture that could be exploited to compromise the availability of virtualized environments.
Mitigation strategies should focus on implementing proper rate limiting for printk messages within the xenmem_add_to_physmap_one function, establishing maximum thresholds for console output during error conditions, and ensuring that foreign page reference operations are properly validated and constrained. System administrators should upgrade to patched versions of Xen, apply appropriate kernel-level mitigations, and monitor console output for unusual patterns that might indicate exploitation attempts. Additionally, implementing proper access controls and limiting the permissions of domains that require memory mapping capabilities can reduce the attack surface and prevent unauthorized exploitation of this vulnerability.