CVE-2012-4444 in Linux
Summary
by MITRE
The ip6_frag_queue function in net/ipv6/reassembly.c in the Linux kernel before 2.6.36 allows remote attackers to bypass intended network restrictions via overlapping IPv6 fragments.
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Analysis
by VulDB Data Team • 04/20/2021
The vulnerability identified as CVE-2012-4444 represents a critical flaw in the Linux kernel's IPv6 fragment reassembly mechanism that fundamentally undermines network security controls. This issue resides within the ip6_frag_queue function located in the net/ipv6/reassembly.c file, which handles the process of reassembling fragmented IPv6 packets. The vulnerability specifically affects Linux kernel versions prior to 2.6.36, creating a significant security gap that adversaries can exploit to circumvent network access controls and firewall rules.
The technical flaw stems from inadequate validation of overlapping IPv6 fragments during the reassembly process. When IPv6 packets exceed the maximum transmission unit of a network path, they must be fragmented into smaller pieces for transmission. The Linux kernel's fragment queue mechanism is responsible for collecting these fragments and reconstructing the original packet. However, the ip6_frag_queue function fails to properly handle cases where overlapping fragments are received, allowing attackers to manipulate the fragment reassembly process. This improper handling occurs because the kernel does not adequately check the boundaries and offsets of fragment data, enabling overlapping regions to be processed without sufficient validation. The vulnerability manifests when an attacker sends carefully crafted overlapping IPv6 fragments that, when processed by the vulnerable kernel, result in a reassembled packet that bypasses normal network filtering mechanisms.
The operational impact of this vulnerability is substantial and far-reaching, particularly in environments where network access control is critical for security. Attackers can exploit this weakness to bypass firewall rules, intrusion detection systems, and other network-based security controls that rely on proper IPv6 fragment handling. The vulnerability enables malicious actors to craft packets that appear to originate from authorized sources while containing payloads that would normally be blocked by network security policies. This capability can be leveraged for various malicious activities including port scanning, protocol exploitation, and data exfiltration attempts that circumvent traditional network defense mechanisms. The impact extends beyond simple access control bypass, as it can potentially enable more sophisticated attacks that rely on fragmented packet delivery to avoid detection by network monitoring tools.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and relates to ATT&CK technique T1071.004 for application layer protocol: DNS, as overlapping fragments can be used to evade detection mechanisms. Organizations running affected Linux kernel versions face significant risk of unauthorized network access and potential data compromise. The vulnerability demonstrates the critical importance of proper input validation in kernel space code, where flaws can have system-wide implications. Network administrators should immediately implement mitigation strategies including kernel updates to versions 2.6.36 or later, which contain the necessary patches to address the fragment reassembly logic. Additionally, implementing network-level restrictions on fragment processing and monitoring for unusual fragment patterns can provide additional defense in depth. The incident underscores the necessity of thorough security testing for kernel components and highlights the importance of maintaining up-to-date system software to protect against known vulnerabilities that could compromise network security posture.