CVE-2017-16995 in Linux
Summary
by MITRE • 01/25/2023
The check_alu_op function in 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 sign extension.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability identified as CVE-2017-16995 resides within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem, specifically in the check_alu_op function located in kernel/bpf/verifier.c. This flaw represents a critical security issue that affects Linux kernel versions through 4.14.8, where the kernel's BPF verifier fails to properly handle sign extension operations during program validation. The vulnerability stems from incorrect implementation of sign extension logic that governs how signed and unsigned integer values are processed within the BPF virtual machine, creating a scenario where maliciously crafted BPF programs can exploit this weakness to manipulate kernel memory structures.
The technical exploitation of this vulnerability occurs through the manipulation of arithmetic and logical operations within BPF programs, where the check_alu_op function incorrectly handles sign extension when processing certain ALU (Arithmetic Logic Unit) operations. When a BPF program is loaded into the kernel, the verifier performs validation to ensure program safety before execution. However, the flaw in sign extension handling allows attackers to craft BPF programs that can bypass these safety checks, leading to memory corruption within kernel space. This improper handling of signed integer operations creates a path where attackers can manipulate the program counter or other kernel memory locations through carefully constructed BPF instructions.
The operational impact of CVE-2017-16995 extends beyond simple denial of service, though that represents the primary consequence. Local attackers with the ability to load BPF programs can trigger memory corruption that may lead to system crashes, kernel panics, or in more sophisticated attack scenarios potentially enable privilege escalation. The vulnerability is particularly dangerous because it operates within kernel space where the attacker's control can directly influence critical system operations. According to CWE classification, this represents a weakness in the BPF verifier's handling of signed integer operations, specifically CWE-191 Integer Underflow/Overflow and CWE-129 Improper Validation. The ATT&CK framework categorizes this under privilege escalation and defense evasion techniques, as attackers can leverage this vulnerability to gain elevated privileges or circumvent kernel security controls.
Mitigation strategies for CVE-2017-16995 focus on both immediate patching and operational security measures. The primary solution involves applying the kernel patch released by the Linux kernel security team, which corrects the sign extension logic in the BPF verifier. Organizations should prioritize updating their kernel versions to 4.14.9 or later, as these releases contain the necessary fixes for the vulnerability. Additionally, system administrators should implement BPF program validation controls and consider restricting BPF program loading capabilities to trusted users only. The vulnerability's impact on system stability means that organizations should also maintain robust monitoring and incident response procedures to detect potential exploitation attempts, particularly focusing on unusual kernel memory patterns or unexpected system crashes that could indicate exploitation of this vulnerability.