CVE-2015-8341 in Xen
Summary
by MITRE
The libxl toolstack library in Xen 4.1.x through 4.6.x does not properly release mappings of files used as kernels and initial ramdisks when managing multiple domains in the same process, which allows attackers to cause a denial of service (memory and disk consumption) by starting domains.
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Analysis
by VulDB Data Team • 06/30/2022
The vulnerability identified as CVE-2015-8341 affects the libxl toolstack library within the Xen hypervisor version 4.1.x through 4.6.x, representing a critical memory management flaw that impacts virtualization environments. This issue stems from improper resource cleanup mechanisms within the library's handling of file mappings used for kernel images and initial ramdisks during domain management operations. The flaw exists specifically when multiple domains are managed within the same process context, creating a scenario where file mappings remain allocated even after domain termination or when new domains are created. This improper resource handling creates a persistent memory leak that can accumulate over time, leading to system instability and resource exhaustion.
The technical implementation of this vulnerability involves the libxl library's failure to properly release memory mappings associated with kernel and ramdisk files when transitioning between domain states. When domains are created and destroyed repeatedly within the same process, the library maintains references to these file mappings in memory, preventing the operating system from reclaiming the associated resources. This behavior manifests as continuous memory consumption that grows with each domain management operation, ultimately leading to system resource exhaustion. The vulnerability operates at the hypervisor level, affecting the core virtualization infrastructure that manages multiple guest operating systems, making it particularly dangerous in cloud computing and virtualized environments where multiple domains are commonly managed simultaneously.
The operational impact of CVE-2015-8341 extends beyond simple resource consumption to create significant denial of service conditions that can compromise entire virtualization platforms. Attackers can exploit this vulnerability by repeatedly starting and stopping domains within the same process, causing progressive memory and disk space consumption until system performance degrades or becomes completely unresponsive. The memory leak affects both physical RAM and disk space utilization as the system accumulates file mapping references that cannot be properly released. This vulnerability particularly impacts cloud service providers and data centers that rely on Xen hypervisors for virtual machine management, as it can lead to cascading failures across multiple virtualized environments. The flaw represents a classic example of resource exhaustion attacks that can be executed with minimal privileges and significant operational impact.
Mitigation strategies for CVE-2015-8341 focus primarily on upgrading to patched versions of the Xen hypervisor where the memory management issues have been resolved through proper resource cleanup mechanisms. Organizations should implement immediate patches to Xen versions 4.7.x and later, which contain the necessary fixes for the libxl toolstack library. Additionally, system administrators should monitor memory and disk usage patterns in virtualized environments to detect early signs of resource exhaustion that may indicate exploitation attempts. The vulnerability aligns with CWE-404, which addresses improper resource release, and demonstrates characteristics consistent with attack patterns documented in the MITRE ATT&CK framework under the resource exhaustion category. Implementation of process isolation techniques and limiting the number of domains managed within single processes can serve as temporary workarounds while permanent patches are deployed. Regular system monitoring and alerting mechanisms should be configured to detect unusual memory consumption patterns that may indicate exploitation of this vulnerability.