CVE-2015-0777 in Xen
Summary
by MITRE
drivers/xen/usbback/usbback.c in linux-2.6.18-xen-3.4.0 (aka the Xen 3.4.x support patches for the Linux kernel 2.6.18), as used in the Linux kernel 2.6.x and 3.x in SUSE Linux distributions, allows guest OS users to obtain sensitive information from uninitialized locations in host OS kernel memory via unspecified vectors.
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Analysis
by VulDB Data Team • 05/02/2022
The vulnerability identified as CVE-2015-0777 represents a critical information disclosure flaw within the Xen hypervisor support patches for the Linux kernel version 2.6.18. This issue specifically affects the usbback driver component located in drivers/xen/usbback/usbback.c within the kernel source tree. The vulnerability exists in the Linux kernel versions 2.6.x and 3.x that incorporate Xen 3.4.x support patches, particularly impacting SUSE Linux distributions that utilize these kernel versions. The flaw allows malicious guest operating system users to extract sensitive data from uninitialized memory locations within the host operating system kernel memory space, creating a significant security risk that spans the virtualization boundary.
The technical root cause of this vulnerability stems from improper initialization of memory buffers within the USB backend driver implementation. When guest operating systems interact with USB devices through the Xen hypervisor, the usbback driver fails to properly initialize certain memory regions before exposing them to guest access. This memory initialization failure creates predictable patterns of uninitialized data that can be read by guest users through various USB communication channels. The vulnerability manifests when the driver processes USB requests from guest VMs without ensuring that all memory locations contain properly initialized values, effectively leaking kernel memory contents to unprivileged guest users. This type of flaw falls under the CWE-128 category of uninitialized memory access, where the system fails to properly initialize memory before use.
The operational impact of CVE-2015-0777 extends beyond simple information disclosure, as it provides attackers with potential access to sensitive kernel memory structures, cryptographic keys, passwords, or other confidential data that may be present in uninitialized memory regions. An attacker operating within a guest VM could potentially reconstruct portions of the host kernel memory, including stack contents, heap data, or other sensitive information that could be leveraged for further exploitation. This vulnerability directly violates the fundamental security principle of isolation between guest and host systems within virtualized environments. The attack vector typically involves crafting specific USB requests that trigger the problematic code path in the usbback driver, allowing the guest to read memory contents that should remain protected within the host kernel space. This represents a classic hypervisor breakout scenario that undermines the security model of virtualization technologies.
Mitigation strategies for this vulnerability require immediate patching of affected kernel versions with the appropriate security fixes that ensure proper memory initialization within the usbback driver. System administrators should prioritize updating their Linux kernel installations to versions that contain the corrected usbback.c implementation, which properly initializes all memory buffers before exposing them to guest access. The fix typically involves modifying the driver code to explicitly initialize memory regions before processing USB requests, preventing the leakage of uninitialized data to guest users. Organizations should also consider implementing additional monitoring to detect unusual USB activity patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving information gathering and privilege escalation through hypervisor vulnerabilities, making it particularly dangerous in multi-tenant cloud environments where guest isolation is paramount for security. Regular security assessments and kernel updates remain essential to prevent exploitation of similar uninitialized memory access vulnerabilities.