CVE-2017-17855 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 improper use of pointers in place of scalars.
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Analysis
by VulDB Data Team • 01/19/2023
The vulnerability identified as CVE-2017-17855 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 arbitrary code execution. The vulnerability stems from improper handling of pointer variables within the BPF verifier's code logic, where pointers are incorrectly used in scalar contexts, creating a dangerous condition that can lead to memory corruption during kernel execution.
The technical nature of this vulnerability involves a type confusion error where the BPF verifier fails to properly validate the data types of variables during program validation. When BPF programs are loaded into the kernel, the verifier performs extensive checks to ensure program safety and prevent malicious code execution. However, in this case, the verifier incorrectly treats pointer values as scalar values in certain conditional branches, leading to unpredictable behavior when the kernel attempts to manipulate these variables. This type confusion creates a memory corruption scenario that can be leveraged to crash the kernel or potentially escalate privileges, as the improper pointer handling can corrupt kernel memory structures and data.
The operational impact of CVE-2017-17855 is significant for any system running affected Linux kernel versions, particularly in environments where local users have access to system resources or can execute code. Local privilege escalation remains a primary concern as attackers can exploit this vulnerability to gain elevated system privileges, potentially allowing them to compromise the entire system. The denial of service aspect of this vulnerability can also be weaponized to create persistent system instability, making affected systems unreliable for critical operations. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and can be categorized under ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities.
Mitigation strategies for CVE-2017-17855 primarily involve applying the official kernel patches released by the Linux kernel community, which address the specific pointer handling issues in the BPF verifier. System administrators should prioritize updating to kernel versions 4.14.9 or later, where the vulnerability has been resolved through proper type validation in the verifier code. Additionally, organizations should implement monitoring to detect suspicious BPF program loading activities and consider disabling BPF functionality if it is not required for system operations. The patch resolves the issue by ensuring proper type checking and validation of pointer variables before they are used in scalar contexts, preventing the memory corruption that enables both denial of service and privilege escalation attacks.