CVE-2015-7754 in ScreenOS
Summary
by MITRE
Juniper ScreenOS before 6.3.0r21, when ssh-pka is configured and enabled, allows remote attackers to cause a denial of service (system crash) or execute arbitrary code via crafted SSH negotiation.
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Analysis
by VulDB Data Team • 11/16/2024
The vulnerability identified as CVE-2015-7754 affects Juniper ScreenOS versions prior to 6.3.0r21 and specifically targets systems with ssh-pka functionality enabled. This issue represents a critical security flaw that can be exploited remotely by attackers to either crash the system or execute malicious code. The vulnerability stems from improper handling of SSH negotiation sequences when the ssh-pka feature is active, creating a pathway for unauthorized remote code execution and system instability. The affected systems typically include Juniper firewalls and security appliances running ScreenOS software, making this a significant concern for network security infrastructure.
The technical root cause of this vulnerability lies in the insufficient validation and processing of SSH protocol negotiation messages when the ssh-pka (SSH Public Key Authentication) feature is enabled. Attackers can craft specially malformed SSH negotiation packets that, when processed by the vulnerable ScreenOS system, trigger memory corruption or improper state handling within the SSH daemon. This flaw falls under CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers buffer overflow vulnerabilities in heap-based memory structures. The improper input validation during SSH key exchange processes creates opportunities for attackers to manipulate memory layouts and potentially execute arbitrary code with system privileges.
The operational impact of CVE-2015-7754 extends beyond simple denial of service scenarios to include full system compromise capabilities. Remote attackers can leverage this vulnerability to gain unauthorized access to network security appliances, potentially leading to complete network infiltration and data exfiltration. The vulnerability is particularly dangerous because it can be exploited without authentication, making it an attractive target for automated attacks. Systems running affected ScreenOS versions become vulnerable to various attack vectors including command execution, privilege escalation, and persistent backdoor installation. This vulnerability directly maps to ATT&CK technique T1021.004, which covers SSH protocol usage for remote access, and T1499.004, which involves network disruption through denial of service attacks.
Organizations should immediately implement mitigation strategies including upgrading to ScreenOS version 6.3.0r21 or later, which contains the necessary patches to address this vulnerability. Alternative mitigations include disabling the ssh-pka feature when not required, implementing network segmentation to limit exposure, and monitoring SSH traffic for anomalous patterns. Security teams should also consider implementing intrusion detection systems that can identify crafted SSH negotiation packets and block them at the network perimeter. The vulnerability demonstrates the importance of proper input validation in cryptographic protocol implementations and highlights the need for comprehensive security testing of network infrastructure components. Organizations with legacy ScreenOS installations should conduct thorough vulnerability assessments and consider migrating to supported security platforms to eliminate exposure to similar vulnerabilities.