CVE-2017-17854 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 (integer overflow and memory corruption) or possibly have unspecified other impact by leveraging unrestricted integer values for pointer arithmetic.
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Analysis
by VulDB Data Team • 01/19/2023
The vulnerability described in CVE-2017-17854 resides within the Linux kernel's eBPF (extended Berkeley Packet Filter) 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 consequences. The vulnerability stems from improper handling of integer values during pointer arithmetic operations within the BPF verification process, which is designed to validate and execute eBPF programs for network packet filtering, tracing, and other kernel-level operations.
The technical flaw manifests as an integer overflow condition that occurs when the BPF verifier processes unrestricted integer values during pointer arithmetic calculations. When an attacker crafts a malicious eBPF program with carefully constructed integer values, the verifier fails to properly validate these values before using them in pointer arithmetic operations. This oversight allows the integer overflow to result in memory corruption, as the arithmetic operations produce unexpected pointer values that can overwrite adjacent memory locations. The vulnerability is particularly dangerous because it operates within kernel space, where such memory corruption can lead to arbitrary code execution or complete system compromise. The issue falls under CWE-190, which classifies integer overflow and underflow conditions, and aligns with ATT&CK technique T1068, which covers exploiting vulnerabilities in the kernel.
The operational impact of this vulnerability extends beyond simple denial of service, as local users can potentially leverage it for privilege escalation or system compromise. The memory corruption resulting from the integer overflow can corrupt kernel data structures, leading to system crashes or allowing attackers to manipulate kernel memory in ways that could enable code execution. Since eBPF programs are designed to be executed with kernel privileges, successful exploitation could provide attackers with elevated access to the system. The vulnerability's exploitation requires local access, but the potential consequences are severe enough to warrant immediate attention from system administrators. The flaw affects systems running affected kernel versions where eBPF functionality is enabled, making it a widespread concern across Linux distributions and server environments that utilize kernel tracing and network filtering capabilities.
Mitigation strategies for CVE-2017-17854 should include immediate kernel updates to versions that contain the patched verifier logic, specifically kernel versions 4.14.9 and later where the integer overflow handling has been corrected. System administrators should also implement runtime restrictions on eBPF program loading through kernel parameters such as disabling eBPF support entirely if the functionality is not required, or limiting the capabilities available to users who can load BPF programs. Additionally, monitoring for unusual BPF program loading activities and implementing proper access controls can help detect potential exploitation attempts. The fix addresses the root cause by implementing proper integer bounds checking before pointer arithmetic operations and ensuring that integer values are validated against expected ranges before being used in kernel memory calculations. Organizations should also consider implementing network segmentation and privilege separation to limit the potential impact of successful exploitation attempts, as the vulnerability's local nature means that attackers must first gain access to the system before attempting exploitation.