CVE-2023-39191 in Linux
Summary
by MITRE • 10/25/2023
An improper input validation flaw was found in the eBPF subsystem in the Linux kernel. The issue occurs due to a lack of proper validation of dynamic pointers within user-supplied eBPF programs prior to executing them. This may allow an attacker with CAP_BPF privileges to escalate privileges and execute arbitrary code in the context of the kernel.
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Analysis
by VulDB Data Team • 07/23/2025
The vulnerability identified as CVE-2023-39191 represents a critical weakness within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem that fundamentally undermines system security through improper input validation. This flaw exists in the kernel's handling of user-supplied eBPF programs where dynamic pointer validation is insufficiently enforced, creating a pathway for privilege escalation attacks that can compromise the entire system. The vulnerability specifically targets the kernel's verification process that should validate all dynamic pointer references within eBPF programs before execution, but fails to properly validate these elements, allowing malicious code to bypass security checks.
The technical implementation of this vulnerability stems from the kernel's eBPF verifier component which is responsible for ensuring that eBPF programs are safe to execute. When eBPF programs contain dynamic pointers that reference memory locations, the verifier should validate these references to prevent unauthorized access or manipulation of kernel memory. However, the flaw allows attackers with CAP_BPF capabilities to craft malicious eBPF programs that exploit this validation gap. This capability directly maps to CWE-122, which describes insufficient validation of pointer references, and aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' through kernel-level vulnerabilities.
The operational impact of this vulnerability is severe as it enables attackers with relatively low privileges to achieve kernel-level code execution, potentially leading to complete system compromise. An attacker with CAP_BPF permissions can leverage this flaw to escalate privileges and execute arbitrary code within the kernel context, bypassing traditional security boundaries. This represents a significant escalation from standard user privileges to full system control, making it particularly dangerous in environments where eBPF capabilities are exposed to untrusted users or applications. The vulnerability effectively undermines the kernel's security model by allowing privilege escalation through legitimate kernel interfaces that should be properly sandboxed.
Mitigation strategies for CVE-2023-39191 should focus on both immediate patching and operational security improvements. The primary solution involves applying the latest kernel updates that contain the necessary fixes for the eBPF verifier's pointer validation mechanisms. Organizations should prioritize patching their Linux systems, particularly those running kernel versions that are vulnerable to this specific flaw. Additionally, implementing least privilege principles for eBPF capabilities can significantly reduce the attack surface, ensuring that only trusted processes have CAP_BPF permissions. System administrators should also consider monitoring for unusual eBPF program loading activities and implementing runtime protections that can detect and prevent exploitation attempts. The mitigation approach should align with security frameworks that emphasize defense in depth, including process isolation, access control enforcement, and continuous monitoring of kernel-level activities to detect potential exploitation attempts.