CVE-2005-0065 in TCP
Summary
by MITRE
The original design of TCP does not check that the TCP sequence number in an ICMP error message is within the range of sequence numbers for data that has been sent but not acknowledged (aka "TCP sequence 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 • 07/01/2021
The vulnerability described in CVE-2005-0065 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 sequence number validation for ICMP error responses, creating a critical security gap that allows malicious actors to exploit the protocol's trust model. The flaw specifically affects how TCP implementations process ICMP error messages such as Destination Unreachable and Source Quench, which are designed to inform senders about network delivery issues. When TCP receives these error messages without proper validation of the sequence number range, it cannot verify whether the error message corresponds to legitimate outstanding data transmission, opening pathways for sophisticated attack vectors.
The technical implementation of this vulnerability manifests through three primary attack patterns that leverage the missing sequence number validation. Attackers can execute blind connection-reset attacks by crafting forged Destination Unreachable ICMP messages that contain sequence numbers corresponding to data that has been sent but not yet acknowledged by the receiving TCP endpoint. This allows them to manipulate TCP state machines into prematurely closing connections or treating legitimate data as invalid. The second attack vector involves blind throughput-reduction using forged Source Quench messages, where attackers manipulate the TCP flow control mechanisms by sending fake congestion notification messages that reduce transmission rates without the receiver actually experiencing network congestion. The third variant targets Path MTU discovery processes through forged ICMP messages that artificially reduce the maximum transmission unit, causing unnecessary packet fragmentation and performance degradation. These attacks exploit the fundamental assumption that ICMP error messages are legitimate and properly associated with active TCP connections.
The operational impact of CVE-2005-0065 extends beyond simple denial of service scenarios to encompass significant network reliability and security concerns. Organizations experiencing these attacks face potential service disruption, performance degradation, and increased network overhead as TCP implementations struggle to handle malformed ICMP responses. The vulnerability affects a broad range of TCP implementations across different operating systems and network equipment, making it particularly dangerous in heterogeneous network environments. From a cybersecurity perspective, this vulnerability aligns with CWE-200, which addresses improper handling of error conditions in network protocols, and represents a classic example of how protocol design flaws can be exploited to compromise availability. The attack patterns correspond to techniques documented in the MITRE ATT&CK framework under network denial of service tactics, specifically targeting TCP/IP stack implementations and network communication reliability.
Mitigation strategies for CVE-2005-0065 require both immediate implementation of sequence number validation and long-term architectural improvements to TCP error handling mechanisms. Network administrators should implement strict validation of ICMP error message sequence numbers within TCP implementations, ensuring that received error messages reference data that has actually been transmitted and not yet acknowledged. The most effective approach involves updating TCP stack implementations to properly validate the sequence number ranges in ICMP error messages against the current send window of active TCP connections. Additionally, network monitoring systems should be enhanced to detect anomalous ICMP error message patterns that might indicate exploitation attempts. Organizations should also consider implementing rate limiting for ICMP error messages and establishing baseline network behavior to identify deviations that could indicate active exploitation. These mitigations align with best practices outlined in RFC 1122 and subsequent TCP protocol specifications that emphasize the importance of proper error message validation in maintaining network protocol integrity and preventing exploitation of fundamental design assumptions.