CVE-2017-17853 in Linux
Summary
by MITRE • 01/25/2023
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 incorrect BPF_RSH signed bounds calculations.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2017-17853 resides within the Linux kernel's Berkeley Packet Filter (BPF) verifier component, specifically in the kernel/bpf/verifier.c file. This flaw affects Linux kernel versions through 4.14.8 and represents a critical security issue that can be exploited by local attackers to cause system instability or potentially achieve more severe outcomes. The vulnerability stems from incorrect signed bounds calculations during the verification process of BPF programs, which are used for network packet filtering, tracing, and other kernel-level operations.
The technical root cause of this vulnerability lies in the BPF verifier's handling of signed integer arithmetic operations, particularly in the BPF_RSH (right shift) instruction. When processing BPF programs, the kernel's verifier attempts to calculate bounds for register values to ensure program safety and prevent memory corruption. However, the implementation contains a flaw in how it handles signed bounds for right shift operations, leading to incorrect calculations that can result in memory corruption when the verifier processes malicious BPF code. This issue is classified under CWE-191, which deals with Integer Underflow or Wraparound, and more specifically relates to improper handling of signed integer operations in bounds checking.
The operational impact of this vulnerability is significant for systems running affected kernel versions, as local users can exploit this weakness to either cause a denial of service through memory corruption or potentially achieve arbitrary code execution. Since BPF programs can be loaded by unprivileged users on systems with appropriate capabilities, this creates a vector for local privilege escalation or system-wide disruption. The memory corruption can manifest in various ways including kernel crashes, data corruption, or potentially allow attackers to manipulate kernel memory structures. Attackers can craft malicious BPF programs that trigger the faulty signed bounds calculation during verification, leading to unpredictable behavior in the kernel's memory management subsystem.
Systems utilizing BPF functionality for network monitoring, security auditing, or performance tracing are particularly at risk, as these applications often run with elevated privileges or are accessible to unprivileged users. The vulnerability can be exploited in environments where BPF programs are frequently loaded or where users have the capability to execute BPF-related system calls such as bpf() with appropriate permissions. The attack surface extends to any system where the kernel's BPF verifier processes user-supplied code, including containers, virtual machines, or systems with network monitoring tools that leverage BPF for packet filtering and inspection. Organizations should consider this vulnerability in their security assessments, particularly in environments where BPF is extensively used for system monitoring or network security functions.
Mitigation strategies include applying the latest kernel updates that contain patches for this vulnerability, which typically involve correcting the signed bounds calculation logic in the BPF verifier. System administrators should also implement proper access controls to limit who can load BPF programs and consider disabling BPF functionality if it is not required for specific use cases. Monitoring for suspicious BPF program loading activities and implementing kernel hardening measures such as kernel address space layout randomization can further reduce the attack surface. Additionally, organizations should review their BPF program deployment practices and ensure that only trusted code is executed through BPF mechanisms, as the vulnerability can be triggered through legitimate BPF program loading operations that appear benign to the system's security controls.