CVE-2023-4881 in Linux
Summary
by MITRE • 09/11/2023
A stack based out-of-bounds write flaw was found in the netfilter subsystem in the Linux kernel. If the expression length is a multiple of 4 (register size), the `nft_exthdr_eval` family of functions writes 4 NULL bytes past the end of the `regs` argument, leading to stack corruption and potential information disclosure or a denial of service.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2023-4881 represents a critical stack-based out-of-bounds write flaw within the netfilter subsystem of the Linux kernel. This issue specifically affects the nft_exthdr_eval family of functions that handle network packet filtering operations. The flaw manifests when processing expressions where the length is a multiple of four bytes, which corresponds to the register size typically used in kernel networking operations. The vulnerability resides in how the kernel handles packet header evaluation within the netfilter framework, which is fundamental to network traffic control and filtering mechanisms across Linux systems.
The technical implementation of this vulnerability stems from improper bounds checking within the nft_exthdr_eval functions that process network packet headers. When an expression length aligns perfectly with the register size of four bytes, the kernel code attempts to write four additional NULL bytes beyond the allocated memory region for the regs argument. This occurs because the memory allocation for the registers structure does not account for the potential boundary conditions that arise when expression lengths are multiples of the register size. The flaw creates a classic stack buffer overflow condition where the program writes beyond the allocated buffer boundaries, corrupting adjacent memory locations on the stack.
The operational impact of CVE-2023-4881 extends beyond simple denial of service scenarios to encompass potential information disclosure and system instability. Attackers who can control the packet filtering rules or manipulate network traffic through the netfilter subsystem could exploit this vulnerability to corrupt kernel memory, potentially leading to privilege escalation or system crashes. The stack corruption could overwrite critical kernel data structures, function return addresses, or other sensitive memory locations, creating opportunities for further exploitation. This vulnerability affects systems running Linux kernels with netfilter functionality, including servers, routers, and network appliances that rely on kernel-based packet filtering for security operations.
Mitigation strategies for CVE-2023-4881 should prioritize immediate kernel updates from vendors to address the underlying buffer management issue. System administrators must ensure all affected Linux distributions receive security patches that correct the bounds checking logic in the nft_exthdr_eval functions. Additional protective measures include implementing network access controls to limit exposure to potentially malicious traffic, monitoring for unusual packet filtering behavior, and applying network segmentation to reduce the attack surface. The vulnerability aligns with CWE-787, which describes out-of-bounds write conditions, and could potentially be leveraged through ATT&CK techniques targeting kernel memory corruption for privilege escalation. Organizations should also conduct comprehensive vulnerability assessments of their network infrastructure to identify systems running affected kernel versions and implement proper patch management procedures to maintain system security.