CVE-2023-4004 in Linux
Summary
by MITRE • 07/31/2023
A use-after-free flaw was found in the Linux kernel's netfilter in the way a user triggers the nft_pipapo_remove function with the element, without a NFT_SET_EXT_KEY_END. This issue could allow a local user to crash the system or potentially escalate their privileges on the system.
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Analysis
by VulDB Data Team • 11/09/2025
The vulnerability identified as CVE-2023-4004 represents a critical use-after-free flaw within the Linux kernel's netfilter subsystem, specifically affecting the nft_pipapo_remove function. This issue resides in the network filtering framework that governs packet handling and access control within the kernel. The flaw manifests when a user-space application invokes the nft_pipapo_remove function without properly initializing or providing the NFT_SET_EXT_KEY_END parameter, creating a dangerous condition where memory previously freed is accessed or manipulated. The netfilter subsystem serves as a fundamental component for packet filtering, network address translation, and traffic control, making this vulnerability particularly concerning for system stability and security. The vulnerability falls under CWE-416, which specifically addresses use-after-free conditions where memory is accessed after being freed, a pattern that frequently leads to system crashes or privilege escalation exploits.
The technical exploitation of this vulnerability requires a local attacker to craft specific netfilter commands that trigger the flawed code path within the nft_pipapo_remove function. When the function executes without the proper NFT_SET_EXT_KEY_END parameter, it attempts to free memory resources that may have already been deallocated or improperly managed, leading to memory corruption. The nature of this use-after-free condition creates opportunities for attackers to manipulate the freed memory location to redirect execution flow or corrupt kernel data structures. This type of vulnerability directly maps to ATT&CK technique T1068, which covers local privilege escalation through the exploitation of kernel vulnerabilities, and T1499, which involves network denial of service attacks that can be initiated through kernel-level flaws. The specific implementation flaw occurs in the pipapo (prefix array) data structure management within the netfilter framework, where the removal operation fails to properly validate the presence of required extension parameters.
The operational impact of CVE-2023-4004 extends beyond simple system crashes to potentially enable privilege escalation, making it a significant concern for systems running Linux kernel versions that include the vulnerable netfilter code. Local users with minimal privileges can leverage this flaw to either cause system instability through kernel crashes or potentially elevate their privileges to root level access, depending on the specific memory corruption patterns and exploitation techniques employed. The vulnerability affects systems where netfilter is actively used for packet filtering, network access control, or firewall configurations, which encompasses a broad range of enterprise and server environments. The attack surface is particularly wide given that netfilter is a core kernel component used extensively in network infrastructure, containerization platforms, and security appliances. When exploited successfully, this vulnerability can result in complete system compromise, data loss, or denial of service conditions that may persist until the system is rebooted or the kernel is patched.
Mitigation strategies for CVE-2023-4004 primarily focus on applying the latest kernel security patches from the vendor, as the vulnerability is addressed through code modifications that properly validate the presence of required parameters before attempting memory operations. System administrators should prioritize patching affected systems, particularly those running kernel versions between 5.10 and 5.19, where this vulnerability was introduced. Additional defensive measures include implementing kernel lockdown mechanisms, restricting local user privileges, and monitoring for suspicious netfilter operations that may indicate exploitation attempts. Network segmentation and access control policies should be reviewed to minimize the attack surface, while security monitoring solutions should be configured to detect anomalous kernel memory access patterns. The vulnerability demonstrates the importance of proper parameter validation in kernel code and highlights the need for comprehensive security testing of core kernel subsystems, particularly those handling memory management and user-space interactions. Organizations should also consider implementing kernel module signing policies and runtime integrity checks to further protect against exploitation of similar vulnerabilities in the future.