CVE-2003-1119 in SSH
Summary
by MITRE
SSH Secure Shell before 3.2.9 allows remote attackers to cause a denial of service via malformed BER/DER packets.
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Analysis
by VulDB Data Team • 07/16/2024
The vulnerability identified as CVE-2003-1119 represents a critical denial of service weakness in SSH Secure Shell implementations prior to version 3.2.9. This flaw specifically targets the handling of malformed Basic Encoding Rules/ Distinguished Encoding Rules packets within the Secure Shell protocol framework. The issue stems from inadequate input validation mechanisms that fail to properly process malformed packet structures, creating opportunities for remote attackers to disrupt service availability. The vulnerability impacts the core authentication and communication mechanisms of SSH implementations, potentially compromising system integrity and availability. This weakness falls under the broader category of improper input validation as classified by CWE-20, which encompasses various scenarios where systems fail to adequately validate or sanitize input data. The attack vector leverages the protocol's parsing logic to trigger unexpected behavior in the SSH daemon processes, making it particularly dangerous in networked environments where SSH services are actively utilized.
The technical exploitation of this vulnerability occurs when remote attackers send specially crafted BER/DER encoded packets to SSH servers running vulnerable versions. These malformed packets contain structures that the SSH implementation cannot properly parse or handle, leading to process crashes or system instability. The vulnerability specifically affects the decoding routines responsible for interpreting the ASN.1 encoded data structures that form part of the SSH protocol's authentication and key exchange mechanisms. When the SSH server encounters these malformed packets during the connection establishment phase, the parsing routines either fail to handle the unexpected data gracefully or process it in ways that cause memory corruption or resource exhaustion. This behavior creates a predictable denial of service condition where legitimate users cannot establish connections to affected SSH services. The vulnerability demonstrates characteristics consistent with CWE-129, improper validation of array indices, and CWE-125, out-of-bounds read conditions, as the parsing logic does not properly validate the boundaries of encoded data structures. The attack requires minimal privileges and can be executed remotely, making it particularly attractive to threat actors seeking to disrupt services without requiring elevated access rights.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall security posture of affected systems. Organizations running vulnerable SSH implementations face risks of unauthorized service interruption that could affect business continuity and system availability. The vulnerability affects the fundamental trust model of SSH communications, as attackers can exploit it to prevent legitimate users from accessing systems while maintaining their own access to the network. This creates a scenario where attackers can effectively lock out legitimate users while continuing to operate within the network infrastructure. The vulnerability also impacts compliance with security standards such as those outlined in the NIST SP 800-53 framework, particularly controls related to system availability and access control. The potential for cascading effects exists when multiple SSH services are deployed across an organization, as a single vulnerable instance could provide attackers with a foothold to compromise additional systems. Security monitoring and incident response capabilities may be strained as administrators attempt to differentiate between legitimate connection failures and attack-induced disruptions. The vulnerability also represents a potential entry point for more sophisticated attacks, as initial denial of service conditions can be used to mask other malicious activities or create opportunities for privilege escalation.
Mitigation strategies for CVE-2003-1119 require immediate implementation of vendor-provided patches and updates to SSH Secure Shell implementations. Organizations should prioritize upgrading to SSH Secure Shell version 3.2.9 or later, which contains the necessary fixes for the malformed BER/DER packet handling issues. Network administrators should implement monitoring solutions to detect unusual connection patterns or packet structures that may indicate exploitation attempts. The implementation of network segmentation and access controls can help limit the potential impact of successful attacks by reducing the attack surface. Security configurations should include disabling unnecessary SSH services and implementing strong access control policies to minimize exposure. Regular vulnerability assessments and penetration testing should be conducted to identify and remediate similar weaknesses in other network services. Organizations should also consider implementing intrusion detection systems capable of identifying malformed packet patterns that could indicate exploitation attempts. The remediation process should include comprehensive testing of updated implementations to ensure that the fixes do not introduce compatibility issues or unintended side effects. System administrators should maintain detailed logs of SSH connection attempts and implement automated alerting for suspicious activities. The vulnerability also highlights the importance of adhering to secure coding practices and conducting thorough code reviews to prevent similar issues in custom implementations. From an ATT&CK framework perspective, this vulnerability aligns with techniques categorized under T1499, Endpoint Termination, and T1566, Phishing, as it can be used to disrupt services and potentially mask other attack activities. Organizations should also consider implementing network-level protections such as firewalls and rate limiting to prevent exploitation attempts from overwhelming vulnerable systems. Regular security awareness training for administrators can help ensure proper configuration and monitoring practices are maintained across all SSH implementations.