CVE-2017-8068 in Linux
Summary
by MITRE
drivers/net/usb/pegasus.c in the Linux kernel 4.9.x before 4.9.11 interacts incorrectly with the CONFIG_VMAP_STACK option, which allows local users to cause a denial of service (system crash or memory corruption) or possibly have unspecified other impact by leveraging use of more than one virtual page for a DMA scatterlist.
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Analysis
by VulDB Data Team • 12/02/2022
The vulnerability identified as CVE-2017-8068 resides within the Linux kernel's networking subsystem, specifically in the pegasus.c driver that manages USB network adapters. This flaw manifests when the kernel is compiled with the CONFIG_VMAP_STACK option enabled, creating a dangerous interaction between virtual memory management and DMA operations. The vulnerability affects Linux kernel versions 4.9.x prior to 4.9.11, representing a critical security gap that could be exploited by local attackers to disrupt system operations. The core issue stems from improper handling of DMA scatterlists when multiple virtual pages are utilized, creating a scenario where memory corruption or system crashes can occur during network data processing.
The technical root cause of this vulnerability lies in how the pegasus USB network driver manages memory mappings when the vmap stack feature is active. When CONFIG_VMAP_STACK is enabled, the kernel uses virtual memory mapping for stack allocation, which changes the memory layout characteristics that the driver expects. The driver incorrectly assumes that DMA scatterlists will utilize a single contiguous virtual page, but when multiple pages are involved due to the vmap stack implementation, the memory management logic fails to properly account for the scattered memory regions. This misalignment creates opportunities for memory corruption when the driver processes network packets through the affected USB interface, particularly when the scatterlist operations span multiple virtual pages.
The operational impact of this vulnerability extends beyond simple denial of service, as it can lead to unpredictable system behavior and potential privilege escalation scenarios. Local attackers with access to the system can trigger the vulnerability by causing network traffic through the affected USB ethernet adapter, potentially leading to system crashes that require manual rebooting or more severe memory corruption that could compromise system integrity. The vulnerability's nature makes it particularly dangerous in environments where system stability is critical, as the denial of service can be both persistent and difficult to diagnose. Additionally, the memory corruption aspects of this flaw could potentially be exploited to gain unauthorized access to system resources or escalate privileges, though direct exploitation for privilege escalation remains challenging without additional attack vectors.
Mitigation strategies for CVE-2017-8068 primarily involve upgrading to Linux kernel versions 4.9.11 or later, where the driver has been patched to properly handle virtual page scenarios when CONFIG_VMAP_STACK is enabled. System administrators should also consider disabling the CONFIG_VMAP_STACK option if the affected driver is in use and virtual stack mapping is not required for the specific deployment. The vulnerability demonstrates the importance of proper memory management in kernel drivers and the potential risks when different kernel features interact in unexpected ways. This issue aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to ATT&CK technique T1068, involving the exploitation of system vulnerabilities for privilege escalation. Organizations should implement comprehensive patch management policies to ensure all systems running affected kernel versions are updated promptly, as the vulnerability affects the fundamental network stack operations that many systems rely upon for connectivity and communication.