CVE-2001-1469 in SSH
Summary
by MITRE
The RC4 stream cipher as used by SSH1 allows remote attackers to modify messages without detection by XORing the original message s cyclic redundancy check (CRC) with the CRC of a mask consisting of all the bits of the original message that were modified.
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Analysis
by VulDB Data Team • 11/17/2024
The vulnerability described in CVE-2001-1469 represents a critical flaw in the implementation of the RC4 stream cipher within SSH version 1.0 protocols, fundamentally undermining the integrity and authenticity guarantees that secure communication protocols are designed to provide. This weakness specifically targets the cryptographic mechanisms used to protect data during transmission, creating a scenario where malicious actors can manipulate transmitted information without being detected by the receiving system. The vulnerability stems from the improper handling of cyclic redundancy checks within the SSH1 framework, which creates a mathematical exploit that allows attackers to modify data packets while maintaining the appearance of valid communication.
The technical flaw manifests through a sophisticated manipulation of the RC4 encryption algorithm's interaction with the CRC integrity checking mechanism. When SSH1 employs RC4 for encryption, the protocol calculates a CRC value for the message before encryption and includes this value in the encrypted payload. However, the vulnerability allows attackers to modify the encrypted data in such a way that when the receiver decrypts the message, the CRC value is altered to match the modified data. This occurs because the XOR operation between the original CRC and a modified mask creates a new CRC that validates against the altered message content. The mathematical relationship between the RC4 keystream and the CRC calculation creates a predictable pattern that attackers can exploit to modify specific bits within the encrypted message while ensuring that the modified CRC remains valid.
The operational impact of this vulnerability extends far beyond simple data corruption, as it fundamentally compromises the security model of SSH1 communications. Attackers can potentially modify sensitive information such as passwords, commands, or data transfers without detection, creating opportunities for unauthorized access and data manipulation. This weakness is particularly dangerous in environments where SSH1 is used for administrative access to critical systems, as it allows attackers to silently alter command sequences or modify authentication credentials. The vulnerability affects the core principle of message integrity that cryptographic protocols are designed to maintain, effectively creating a backdoor for man-in-the-middle attacks and data tampering scenarios that can persist undetected within network communications.
Mitigation strategies for this vulnerability require immediate protocol upgrades and architectural changes to address the fundamental design flaw in SSH1's cryptographic implementation. Organizations must transition from SSH1 to SSH2 protocols, which implement more robust cryptographic mechanisms and eliminate the mathematical vulnerabilities present in SSH1. The recommended approach involves comprehensive network auditing to identify systems still using SSH1, followed by mandatory protocol upgrades and security policy updates. Additionally, network administrators should implement monitoring solutions that can detect anomalous behavior patterns consistent with this type of attack, as well as establish proper key management practices that include regular cryptographic algorithm assessments. This vulnerability aligns with CWE-310, which addresses cryptographic weaknesses, and represents a clear example of how improper implementation of cryptographic primitives can create exploitable security gaps. The attack vector described in this vulnerability maps to ATT&CK technique T1071.004, which covers protocol tunneling and data manipulation in secure communications, highlighting the need for comprehensive network security monitoring and incident response procedures to detect and respond to such attacks effectively.