CVE-2017-17856 in Linux
Summary
by MITRE
kernel/bpf/verifier.c in the Linux kernel through 4.14.8 allows local users to cause a denial of service (memory corruption) or possibly have unspecified other impact by leveraging the lack of stack-pointer alignment enforcement.
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Analysis
by VulDB Data Team • 01/19/2023
The vulnerability identified as CVE-2017-17856 resides within the Linux kernel's Berkeley Packet Filter (BPF) subsystem, specifically in the verifier.c file that governs the validation of eBPF programs before execution. This flaw represents a critical memory corruption issue that affects Linux kernel versions up to 4.14.8, creating a potential pathway for local attackers to compromise system stability and potentially execute arbitrary code. The BPF subsystem serves as a powerful virtual machine for network packet filtering and tracing, making it a crucial component for system security and monitoring operations.
The technical root cause of this vulnerability stems from insufficient stack-pointer alignment enforcement during BPF program verification. When eBPF programs are loaded into the kernel, the verifier component performs extensive checks to ensure program safety and prevent malicious code execution. However, this particular flaw fails to properly validate stack pointer alignment, which creates a condition where the kernel's memory management can become corrupted. The lack of proper alignment enforcement allows for misaligned memory access patterns that can lead to unpredictable behavior and system instability. This issue falls under the CWE-121 category of stack-based buffer overflow conditions, though it manifests specifically within the kernel's BPF verification context.
The operational impact of CVE-2017-17856 extends beyond simple denial of service scenarios, as local users with limited privileges can exploit this weakness to cause system crashes or potentially escalate their privileges. The vulnerability enables attackers to craft malicious eBPF programs that, when executed, can corrupt kernel memory structures and cause system-wide instability. This represents a significant concern for systems that rely heavily on BPF for network monitoring, security policy enforcement, or system tracing operations. The attack vector requires local access to the system, but the consequences can be severe enough to compromise the entire system's integrity and availability, making it particularly dangerous in multi-tenant environments or systems where privilege separation is not strictly enforced.
Mitigation strategies for this vulnerability should prioritize immediate kernel updates to versions 4.14.9 or later where the stack-pointer alignment enforcement has been properly implemented. System administrators should also implement monitoring solutions to detect suspicious BPF program loading activities and consider restricting BPF program capabilities through kernel parameters or security modules. The ATT&CK framework categorizes this vulnerability under T1059.007 for kernel modules and drivers, while the exploitability requires local system access and leverages privilege escalation techniques through memory corruption. Organizations should also consider implementing the principle of least privilege for BPF program execution and regularly audit BPF program usage to prevent unauthorized loading of potentially malicious code. Additionally, the vulnerability highlights the importance of proper memory alignment validation in kernel-space code and serves as a reminder of the critical security implications of seemingly minor verification flaws in core system components.