CVE-2005-3945 in Windows
Summary
by MITRE
The SynAttackProtect protection in Microsoft Windows 2003 before SP1 and Windows 2000 before SP4 with Update Roll-up uses a hash of predictable data, which allows remote attackers to cause a denial of service (CPU consumption) via a flood of SYN packets that produce identical hash values, which slows down the hash table lookups.
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Analysis
by VulDB Data Team • 06/16/2019
The vulnerability described in CVE-2005-3945 represents a critical weakness in the TCP SYN flood protection mechanism implemented in Microsoft Windows 2000 and Windows 2003 operating systems prior to their respective service packs. This flaw specifically impacts the SynAttackProtect feature which was designed to mitigate SYN flood attacks by implementing a hash table-based mechanism to track incoming connection requests. The protection system employs a hashing algorithm to categorize incoming SYN packets and manage them efficiently in memory. However, the implementation suffers from a fundamental design flaw where the hash function utilizes predictable data elements from the network packets, creating a scenario where attackers can deliberately craft packets that all map to the same hash bucket.
The technical implementation of this vulnerability stems from the use of a non-cryptographic hash function that processes predictable packet headers such as source IP addresses and port numbers in a deterministic manner. When attackers flood the system with SYN packets that share identical or highly correlated predictable values, they can force multiple packets into the same hash bucket, effectively creating hash collisions. This condition transforms what should be an efficient O(1) hash table lookup operation into a linear search through a chain of entries, dramatically increasing CPU utilization and system resource consumption. The vulnerability specifically affects systems running Windows 2000 before SP4 and Windows 2003 before SP1, where the hash table implementation lacks proper collision handling mechanisms.
The operational impact of this vulnerability manifests as a significant degradation in system performance and potential complete denial of service conditions. Attackers can consume system resources at an exponential rate by sending a relatively small number of specially crafted SYN packets that all produce identical hash values. This attack vector is particularly dangerous because it requires minimal computational resources from the attacker while generating maximum impact on the target system. The CPU consumption increases dramatically as the hash table becomes increasingly congested with entries that hash to the same location, causing the system to spend excessive time processing these collisions rather than handling legitimate network traffic. The vulnerability affects the core network stack functionality and can render affected systems unusable for legitimate users while maintaining the appearance of normal operation.
The mitigation strategies for this vulnerability primarily involve applying the appropriate service packs and updates released by Microsoft to address the hash collision issue. Microsoft released Windows 2000 SP4 and Windows 2003 SP1 which included improved hash table implementations that use more robust hashing algorithms and better collision handling mechanisms. Organizations should also implement additional network-level protections such as SYN cookies, rate limiting, and firewall rules to prevent excessive SYN packet flooding. From a cybersecurity perspective, this vulnerability aligns with CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and CWE-254 (Security Features in the System are Not Properly Configured) categories, as it represents both a flawed cryptographic implementation and improper security configuration. The attack pattern follows ATT&CK technique T1498.001 (Network Denial of Service) and can be classified under T1595.001 (Network Denial of Service) within the adversary tactics and techniques framework. Organizations should also consider implementing intrusion detection systems that can identify and alert on abnormal SYN packet patterns that may indicate this specific attack vector.