CVE-2019-7308 in Linux
Summary
by MITRE
kernel/bpf/verifier.c in the Linux kernel before 4.20.6 performs undesirable out-of-bounds speculation on pointer arithmetic in various cases, including cases of different branches with different state or limits to sanitize, leading to side-channel attacks.
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Analysis
by VulDB Data Team • 07/04/2023
The vulnerability identified as CVE-2019-7308 resides within the Linux kernel's BPF (Berkeley Packet Filter) verifier component, specifically in the kernel/bpf/verifier.c file. This issue affects Linux kernel versions prior to 4.20.6 and represents a critical security flaw that exploits speculative execution mechanisms to enable side-channel attacks. The vulnerability stems from improper handling of pointer arithmetic operations during BPF program verification, creating conditions where out-of-bounds memory accesses can occur speculatively, potentially exposing sensitive information through timing side channels.
The technical flaw manifests when the BPF verifier processes programs that contain pointer arithmetic operations with different branch states or varying sanitization limits. During speculative execution, the kernel's verifier may attempt to access memory locations that are beyond the bounds of valid program data structures. This occurs because the verification logic does not adequately account for the potential for out-of-bounds speculation when evaluating different execution paths within BPF programs. The vulnerability specifically impacts the kernel's handling of pointer arithmetic in conditional branches where the verifier must maintain different state information for each path, creating opportunities for speculative execution to access unauthorized memory regions.
The operational impact of this vulnerability is significant as it allows attackers to potentially extract sensitive information from kernel memory through side-channel attacks. The speculative execution behavior enables adversaries to observe timing differences that reveal information about memory contents, particularly when different execution paths lead to varying memory access patterns. This type of vulnerability falls under the broader category of speculative execution side-channel attacks and aligns with attack patterns described in the MITRE ATT&CK framework under techniques such as speculative execution side-channel attacks. The vulnerability can be exploited by malicious BPF programs running on systems with vulnerable kernel versions, potentially leading to privilege escalation or information disclosure attacks.
This vulnerability is classified as a software fault that can be mapped to CWE-126 (Buffer Over-read) and CWE-129 (Improper Validation of Array Index) within the CWE taxonomy, as it involves improper bounds checking during pointer arithmetic operations. The issue demonstrates the complexity of modern kernel security where the interaction between hardware speculative execution features and software verification logic can create unexpected attack vectors. The BPF subsystem is commonly used for network packet filtering, system call tracing, and other performance monitoring tasks, making this vulnerability particularly dangerous as it affects core kernel functionality. The vulnerability's exploitation requires an attacker to have the ability to load and execute BPF programs, which may be possible in certain contexts such as containers or applications that utilize BPF for legitimate purposes.
Mitigation strategies for CVE-2019-7308 primarily involve upgrading to Linux kernel version 4.20.6 or later, where the BPF verifier has been patched to properly handle pointer arithmetic and prevent out-of-bounds speculation. System administrators should also consider implementing additional security controls such as restricting BPF program loading capabilities where possible, monitoring for unusual BPF activity, and ensuring that systems are regularly updated with the latest kernel security patches. Organizations should also review their BPF program deployment practices and consider implementing runtime monitoring to detect potential exploitation attempts. The patch addresses the underlying verification logic to ensure that pointer arithmetic operations maintain proper bounds checking even during speculative execution phases, preventing the conditions that lead to out-of-bounds memory access patterns.