CVE-2017-17864 in Linux
Summary
by MITRE
kernel/bpf/verifier.c in the Linux kernel through 4.14.8 mishandles states_equal comparisons between the pointer data type and the UNKNOWN_VALUE data type, which allows local users to obtain potentially sensitive address information, aka a "pointer leak."
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Analysis
by VulDB Data Team • 01/19/2023
The vulnerability identified as CVE-2017-17864 resides within the Linux kernel's Berkeley Packet Filter (BPF) subsystem, specifically in the verifier component located at kernel/bpf/verifier.c. This flaw affects Linux kernel versions through 4.14.8 and represents a critical security issue that enables local privilege escalation through information disclosure. The BPF subsystem serves as a powerful virtual machine for filtering network packets and executing sandboxed programs, making it a crucial component in kernel security architecture. The vulnerability manifests during the verification process when the kernel attempts to compare pointer data types against UNKNOWN_VALUE data types, creating an exploitable condition that can leak sensitive memory addresses.
The technical root cause of this vulnerability stems from improper handling of state comparisons within the BPF verifier's state management system. When the verifier processes BPF programs, it maintains internal state information about variables and their types during program analysis. The flaw occurs specifically in the states_equal function where the comparison logic fails to properly account for the interaction between pointer types and UNKNOWN_VALUE types. This improper state comparison allows the verifier to potentially reveal memory addresses that should remain hidden from user-space programs, effectively leaking kernel memory information. The issue is classified as a pointer leak because the vulnerability enables attackers to indirectly obtain sensitive address information that could be used in more sophisticated exploitation techniques.
From an operational perspective, this vulnerability presents significant risks to systems running affected kernel versions, as local users can exploit it to gain access to kernel memory addresses that may be used in subsequent attacks. The information disclosure aspect means that an attacker with local access could potentially use the leaked addresses to bypass kernel address space layout randomization (ASLR) protections, which are fundamental security mechanisms designed to prevent exploitation. The vulnerability's impact extends beyond simple information disclosure, as the leaked memory addresses could enable more advanced exploitation techniques such as return-oriented programming (ROP) or jump-oriented programming (JOP) attacks that rely on knowing specific memory locations. This makes the vulnerability particularly dangerous in environments where local users might not have direct access to sensitive systems but could potentially gain access through other means.
Mitigation strategies for CVE-2017-17864 primarily involve upgrading to kernel versions that contain the patched implementation, specifically kernel versions 4.14.9 and later. System administrators should prioritize updating their kernel installations to eliminate the risk of exploitation, as the vulnerability affects the core kernel functionality and cannot be effectively mitigated through configuration changes alone. Additionally, implementing proper access controls and limiting local user privileges can help reduce the attack surface, though these measures do not fully protect against exploitation. The vulnerability demonstrates the importance of thorough state management in kernel code and highlights the need for comprehensive testing of edge cases in verifier implementations. Organizations should also consider monitoring for suspicious BPF program loading activities and implementing kernel hardening techniques such as stack canaries and kernel module signing to further protect against potential exploitation attempts. This vulnerability aligns with CWE-248, which covers "Uncaught Exception in BPF Verifier," and represents a significant concern in the ATT&CK framework under privilege escalation techniques where information disclosure serves as a prerequisite for more sophisticated attacks.