CVE-2016-1907 in OpenSSH
Summary
by MITRE
The ssh_packet_read_poll2 function in packet.c in OpenSSH before 7.1p2 allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via crafted network traffic.
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Analysis
by VulDB Data Team • 07/03/2022
The vulnerability identified as CVE-2016-1907 represents a critical out-of-bounds read condition within the OpenSSH implementation that affects versions prior to 7.1p2. This flaw exists within the ssh_packet_read_poll2 function located in the packet.c source file, which forms a core component of the SSH protocol handling mechanism. The vulnerability arises from insufficient input validation and boundary checking during packet processing, creating a scenario where maliciously crafted network traffic can trigger memory access violations.
The technical nature of this vulnerability stems from improper handling of packet length fields in the SSH protocol implementation. When the ssh_packet_read_poll2 function processes incoming network packets, it fails to adequately validate the packet size indicators before attempting to read data from memory locations. This allows attackers to construct specially crafted packets that contain malformed length values, causing the function to attempt reading beyond the allocated buffer boundaries. The out-of-bounds memory access results in undefined behavior that can manifest as application crashes or memory corruption, effectively enabling a denial of service condition.
From an operational perspective, this vulnerability presents significant risk to systems running vulnerable OpenSSH versions as it can be exploited remotely without authentication requirements. Attackers can simply send malformed SSH packets to target systems, causing the sshd daemon to crash and terminate the service. This creates a persistent denial of service condition that can be repeated indefinitely, making it particularly dangerous for critical infrastructure and network services that rely on SSH connectivity. The vulnerability impacts both server and client implementations, though the most significant operational impact occurs when the server process is compromised.
The security implications extend beyond simple service disruption as this vulnerability can serve as a precursor to more sophisticated attacks. According to the CWE taxonomy, this represents a CWE-129: Improper Validation of Array Index vulnerability, where the system fails to validate that array indices are within acceptable ranges. Additionally, from an ATT&CK framework perspective, this vulnerability maps to T1499.004: Endpoint Denial of Service, where adversaries can disrupt services by exploiting resource consumption issues. The vulnerability also aligns with T1566.001: Phishing, as attackers may use this to compromise SSH servers and gain unauthorized access to systems. Organizations should prioritize patching this vulnerability as it can be exploited by automated scanning tools and represents a low-effort, high-impact attack vector.
Mitigation strategies should include immediate deployment of OpenSSH version 7.1p2 or later, which contains the necessary patches to address the buffer boundary checking issues. System administrators should also implement network-level filtering to monitor and restrict suspicious SSH traffic patterns, though this approach provides only partial protection as the vulnerability can be exploited through various network configurations. Additionally, organizations should consider implementing intrusion detection systems that can identify anomalous packet patterns consistent with this exploit. Regular security audits and vulnerability assessments should be conducted to ensure all SSH implementations remain up-to-date with security patches, as this vulnerability demonstrates the importance of timely patch management in maintaining secure network services.