CVE-2006-0037 in Linux
Summary
by MITRE
ip_nat_pptp in the PPTP NAT helper (netfilter/ip_nat_helper_pptp.c) in Linux kernel 2.6.14, and other versions, allows local users to cause a denial of service (memory corruption or crash) via a crafted outbound packet that causes an incorrect offset to be calculated from pointer arithmetic when non-linear SKBs (socket buffers) are used.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability described in CVE-2006-0037 resides within the Linux kernel's netfilter subsystem, specifically in the PPTP NAT helper module known as ip_nat_pptp. This flaw affects kernel versions including 2.6.14 and earlier releases, representing a critical memory corruption issue that can be exploited to trigger system crashes or denial of service conditions. The vulnerability manifests when the kernel processes outbound packets through the PPTP NAT helper, which is responsible for handling Point-to-Point Tunneling Protocol traffic that requires network address translation. The core issue stems from improper pointer arithmetic calculations when handling non-linear socket buffers, which are memory structures used by the kernel to efficiently manage packets that exceed the typical buffer size limits. This particular flaw falls under the Common Weakness Enumeration category of CWE-121, which describes heap-based buffer overflow conditions, and more specifically relates to CWE-787, representing out-of-bounds write vulnerabilities that can result in memory corruption. The attack vector requires local user privileges to execute, making it a privilege escalation vulnerability that can be leveraged to cause system instability. When a malicious user crafts specific outbound packets designed to trigger this condition, the kernel's pointer arithmetic logic incorrectly calculates memory offsets, leading to memory corruption that can ultimately result in kernel crashes or system panics.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it represents a potential pathway for more sophisticated attacks that could exploit the memory corruption to gain unauthorized access to system resources. The vulnerability specifically targets the handling of non-linear SKBs, which are socket buffers that are fragmented across multiple memory pages to accommodate large packets, making the exploitation more complex but also more impactful. When the kernel encounters such packets through the PPTP NAT helper, the incorrect offset calculation can overwrite critical kernel memory regions, potentially corrupting data structures or even allowing for arbitrary code execution if the corruption affects control flow mechanisms. This vulnerability directly aligns with the MITRE ATT&CK framework under the technique T1068, which covers "Exploitation for Privilege Escalation," and T1499, covering "Endpoint Denial of Service," as the local user can leverage this flaw to disrupt system operations. The affected kernel version range indicates this was a long-standing issue that affected numerous Linux distributions and could potentially be exploited across various network environments where PPTP tunneling was in use. The nature of the flaw means that any system running affected kernel versions and utilizing PPTP NAT helper functionality would be vulnerable to this memory corruption issue.
Mitigation strategies for this vulnerability primarily involve kernel version updates and system patching, as the most effective solution requires addressing the root cause in the kernel source code. System administrators should immediately apply security patches from their respective Linux distributions to upgrade to kernel versions that contain the corrected pointer arithmetic logic within the ip_nat_pptp module. Additionally, network administrators should consider disabling PPTP NAT helper functionality if the service is not actively required, as this eliminates the attack surface for this specific vulnerability. The implementation of proper input validation and bounds checking in the kernel's network handling code provides a more fundamental approach to preventing such memory corruption issues. Organizations should also implement monitoring solutions to detect unusual network traffic patterns that might indicate exploitation attempts, particularly focusing on outbound packets that could trigger the specific non-linear SKB handling code path. Security teams should consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and other exploit mitigations that can reduce the effectiveness of potential exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date kernel versions and implementing comprehensive security practices across all system components, as this flaw could potentially be chained with other vulnerabilities to create more sophisticated attack scenarios. Regular security audits and vulnerability assessments should include checks for outdated kernel versions and unnecessary network services that could expose systems to similar memory corruption vulnerabilities.