CVE-2007-0244 in PPTP Server
Summary
by MITRE
pptpgre.c in PoPToP Point to Point Tunneling Server (pptpd) before 1.3.4 allows remote attackers to cause a denial of service (PPTP connection tear-down) via (1) GRE packets with out-of-order sequence numbers or (2) certain GRE packets that are processed using a wrong pointer and improperly dequeued.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2007-0244 affects the Point to Point Tunneling Protocol implementation within the PoPToP Point to Point Tunneling Server version 1.3.3 and earlier. This flaw exists in the pptpgre.c component which handles Generic Routing Encapsulation processing for PPTP connections. The vulnerability represents a significant security concern as it can be exploited by remote attackers to disrupt network connectivity through deliberate denial of service attacks against PPTP services.
The technical implementation flaw stems from improper handling of GRE packets within the PPTP connection management system. Specifically, the vulnerability manifests in two distinct attack vectors that exploit memory management and packet processing errors. The first vector involves GRE packets containing out-of-order sequence numbers that trigger unexpected behavior in the packet processing logic. The second vector exploits a scenario where certain GRE packets are processed using incorrect memory pointers, leading to improper dequeuing operations that corrupt the connection state management structures.
When exploited, these vulnerabilities result in the complete tearing down of PPTP connections, effectively rendering the tunneling service unavailable to legitimate users. The impact extends beyond simple service disruption as it can be leveraged to systematically degrade network access for users relying on PPTP-based VPN connections. This type of attack directly violates the availability principle of the CIA triad and can be particularly damaging in enterprise environments where PPTP is used for remote access connectivity.
From an operational perspective, this vulnerability creates a persistent threat to network infrastructure security as it requires minimal privileges to exploit and can be automated to target multiple systems. The attack vectors align with techniques described in the ATT&CK framework under network denial of service tactics, specifically targeting network service availability. Organizations using older versions of PoPToP are particularly vulnerable as the flaw exists in core connection management logic that handles critical network traffic processing.
The vulnerability demonstrates poor memory management practices that are categorized under CWE-129, which addresses improper handling of buffer boundaries, and CWE-476, which covers null pointer dereference conditions. These weaknesses in the codebase indicate insufficient input validation and memory safety checks that are fundamental requirements for secure network service implementations. The improper pointer usage and incorrect dequeuing operations suggest inadequate error handling mechanisms that should be present in production-grade network services.
Mitigation strategies for this vulnerability require immediate patching of PoPToP installations to version 1.3.4 or later where the memory management issues have been addressed. Network administrators should also implement monitoring solutions to detect unusual packet patterns that might indicate exploitation attempts. Additional defensive measures include implementing network segmentation to limit exposure, deploying intrusion detection systems that can identify malformed GRE packet sequences, and ensuring proper access controls on PPTP services to minimize attack surface. Organizations should also consider migrating away from PPTP protocol due to its known security limitations and replace it with more modern and secure VPN protocols such as IPsec or OpenVPN that provide better security guarantees and are less susceptible to similar memory corruption vulnerabilities.