CVE-2008-5849 in VPN-1
Summary
by MITRE
Check Point VPN-1 R55, R65, and other versions, when Port Address Translation (PAT) is used, allows remote attackers to discover intranet IP addresses via a packet with a small TTL, which triggers an ICMP_TIMXCEED_INTRANS (aka ICMP time exceeded in-transit) response containing an encapsulated IP packet with an intranet address, as demonstrated by a TCP packet to the firewall management server on port 18264.
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Analysis
by VulDB Data Team • 10/23/2018
This vulnerability in Check Point VPN-1 R55 and R65 represents a significant information disclosure flaw that exploits the interaction between Port Address Translation and ICMP error handling mechanisms. The vulnerability occurs when the firewall processes packets with small TTL values, specifically those that will expire during transit, triggering ICMP time exceeded responses that contain encapsulated IP packets with internal network addresses. This behavior fundamentally violates network security principles by exposing internal IP addressing schemes to external attackers who can leverage this information for further reconnaissance and targeted attacks. The vulnerability is particularly concerning because it affects the core network protection functionality of the firewall, potentially providing attackers with critical intelligence about internal network topology and address space.
The technical flaw stems from the improper handling of ICMP time exceeded messages when PAT is enabled on the firewall. When a packet with a small TTL value is processed, the firewall generates an ICMP_TIMXCEED_INTRANS response that includes the original packet payload, which in this case contains internal IP addresses from the intranet. This occurs because the firewall does not properly sanitize or filter the encapsulated packet data within the ICMP response before sending it to the attacker. The vulnerability is specifically demonstrated against the firewall management server port 18264, which suggests that the management interface may be particularly susceptible to this information disclosure attack. This type of flaw falls under CWE-200, Information Exposure, and demonstrates poor input validation and output sanitization practices in network security devices.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with a method to map internal network structures and identify potentially vulnerable internal systems. Attackers can use this information to craft more sophisticated attacks by targeting specific internal IP addresses, potentially bypassing additional network security controls that rely on the obscurity of internal addressing schemes. The vulnerability affects multiple versions of Check Point VPN-1, indicating it was likely present in the core architecture and not just a specific implementation bug, making it a widespread concern across affected deployments. This weakness aligns with ATT&CK technique T1082, System Information Discovery, and T1046, Network Service Scanning, as it enables attackers to gather system and network information that would otherwise remain hidden.
Organizations using affected Check Point VPN-1 versions should implement immediate mitigations to address this vulnerability. The primary recommendation involves disabling or carefully configuring PAT functionality when it is not strictly required, as this removes the attack vector entirely. Network administrators should also consider implementing additional filtering rules to prevent ICMP time exceeded messages from being sent to external hosts, or at minimum, ensure that the encapsulated data within these responses does not contain sensitive internal IP addresses. The vulnerability demonstrates the critical importance of proper input validation and output sanitization in network security appliances, as it shows how a seemingly benign ICMP handling mechanism can become a security liability when not properly secured. Regular security assessments and updates to network security infrastructure are essential to prevent similar vulnerabilities from being exploited in production environments.