CVE-2006-0036 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 remote attackers to cause a denial of service (memory corruption or crash) via an inbound PPTP_IN_CALL_REQUEST packet that causes a null pointer to be used in an offset calculation.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability described in CVE-2006-0036 represents a critical memory corruption issue within the Linux kernel's network packet handling mechanisms, specifically affecting the PPTP NAT helper component. This flaw exists in the netfilter/ip_nat_helper_pptp.c file and impacts kernel versions including 2.6.14 and other subsequent releases. The vulnerability manifests when the system processes inbound PPTP_IN_CALL_REQUEST packets, which are part of the Point-to-Point Tunneling Protocol used for establishing VPN connections. The issue stems from improper validation of packet data structures before memory operations are performed.
The technical exploitation of this vulnerability occurs through a specific sequence of packet processing that leads to a null pointer dereference during offset calculations within the PPTP NAT helper module. When a malicious remote attacker sends a specially crafted PPTP_IN_CALL_REQUEST packet, the kernel's packet processing code fails to properly validate the packet header fields before attempting arithmetic operations on pointer values. This results in the system attempting to calculate offsets using null pointers, which ultimately leads to memory corruption and system instability. The vulnerability is classified as a null pointer dereference, which is a common pattern for denial of service exploits and can potentially lead to system crashes or memory corruption that might be exploitable for privilege escalation.
The operational impact of this vulnerability extends beyond simple denial of service conditions as it affects the core networking functionality of affected Linux systems. Systems utilizing PPTP VPN connections or those with netfilter-based NAT configurations are particularly vulnerable, as the attack can be executed remotely without authentication requirements. The memory corruption resulting from this flaw can cause unpredictable system behavior, including kernel panics, system reboots, and potential data loss. Network administrators managing corporate environments with PPTP VPN infrastructure face significant risk, as this vulnerability could be exploited to disrupt network services and compromise availability of critical communication channels.
Mitigation strategies for this vulnerability require immediate kernel updates to versions containing the patched PPTP NAT helper implementation. System administrators should prioritize patch management procedures to ensure all affected systems receive security updates promptly. Additionally, network segmentation and access control measures can help reduce exposure by limiting direct access to systems running PPTP services. The vulnerability aligns with CWE-476, which describes null pointer dereference conditions, and represents a classic example of how improper input validation can lead to memory corruption issues. From an ATT&CK perspective, this vulnerability could be categorized under privilege escalation and denial of service tactics, as it provides potential attackers with methods to disrupt system operations and potentially gain unauthorized access to network resources. Organizations should implement comprehensive monitoring to detect unusual packet patterns and maintain updated security baselines to prevent exploitation of this and similar network protocol vulnerabilities.