CVE-2005-0066 in TCP
Summary
by MITRE
The original design of TCP does not check that the TCP Acknowledgement number in an ICMP error message generated by an intermediate router is within the range of possible values for data that has already been acknowledged (aka "TCP acknowledgement number checking"), which makes it easier for attackers to forge ICMP error messages for specific TCP connections and cause a denial of service, as demonstrated using (1) blind connection-reset attacks with forged "Destination Unreachable" messages, (2) blind throughput-reduction attacks with forged "Source Quench" messages, or (3) blind throughput-reduction attacks with forged ICMP messages that cause the Path MTU to be reduced. NOTE: CVE-2004-0790, CVE-2004-0791, and CVE-2004-1060 have been SPLIT based on different attacks; CVE-2005-0065, CVE-2005-0066, CVE-2005-0067, and CVE-2005-0068 are related identifiers that are SPLIT based on the underlying vulnerability. While CVE normally SPLITs based on vulnerability, the attack-based identifiers exist due to the variety and number of affected implementations and solutions that address the attacks instead of the underlying vulnerabilities.
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Analysis
by VulDB Data Team • 06/30/2021
The vulnerability described in CVE-2005-0066 represents a fundamental flaw in the Transmission Control Protocol's handling of Internet Control Message Protocol error messages. This weakness stems from the original TCP specification's omission of validation checks for TCP acknowledgment numbers within ICMP error messages generated by intermediate network routers. The absence of proper range validation creates a significant security gap that allows malicious actors to exploit the protocol's design limitations. This vulnerability specifically affects the TCP stack's interpretation of ICMP error messages, particularly those generated in response to TCP traffic, and enables attackers to manipulate connection states through forged network messages.
The technical implementation of this vulnerability occurs at the network layer where TCP implementations fail to verify that acknowledgment numbers in ICMP error messages fall within acceptable ranges for acknowledged data. When routers encounter TCP packets that cannot be processed, they generate ICMP error messages such as "Destination Unreachable" or "Source Quench" to notify the originating host. However, the TCP stack does not validate whether the acknowledgment numbers referenced in these error messages correspond to legitimate acknowledged data within the connection's sequence space. This validation gap allows attackers to craft ICMP error messages with carefully selected acknowledgment numbers that appear legitimate to the receiving TCP implementation, thereby enabling various forms of attack.
The operational impact of this vulnerability manifests through multiple attack vectors that exploit the lack of TCP acknowledgment number validation. The most significant threat involves blind connection-reset attacks where attackers forge "Destination Unreachable" ICMP messages to force TCP connections to terminate unexpectedly. Additionally, the vulnerability enables blind throughput-reduction attacks through forged "Source Quench" messages that artificially limit network bandwidth allocation. The most insidious aspect involves ICMP messages that manipulate Path MTU (Maximum Transmission Unit) values, causing network fragmentation and performance degradation. These attacks can be executed without requiring direct network access to the target system, making them particularly dangerous as they can be launched from remote locations.
This vulnerability directly relates to CWE-20, "Improper Input Validation," and CWE-225, "Rarely-Used or Obsolete Features in Web Applications," as it represents a failure to properly validate input data from external sources. The attack patterns align with several MITRE ATT&CK techniques including T1498, "Network Denial of Service," and T1071.004, "Application Layer Protocol: DNS." The vulnerability's exploitation demonstrates how protocol-level weaknesses can be leveraged for denial of service attacks, with the original TCP specification failing to account for malicious manipulation of error reporting mechanisms. The attack vectors described in CVE-2005-0066 are particularly concerning because they exploit the trust relationship between network components and the TCP stack, allowing attackers to manipulate connection states without requiring authentication or privileged access.
Mitigation strategies for CVE-2005-0066 focus on implementing proper TCP acknowledgment number validation within network stack implementations. System administrators should ensure that all TCP implementations include comprehensive validation of acknowledgment numbers in ICMP error messages, verifying that these values fall within legitimate ranges for acknowledged data. Network administrators can deploy intrusion detection systems that monitor for anomalous ICMP error message patterns and implement rate limiting for ICMP messages to prevent abuse. The most effective long-term solution involves updating TCP stack implementations to include proper validation mechanisms that check the legitimacy of acknowledgment numbers in ICMP error messages, ensuring that these values correspond to actual acknowledged data within the TCP connection's sequence space. Additionally, implementing proper network segmentation and firewall rules can help limit the impact of such attacks by restricting ICMP message processing to trusted network segments.