CVE-2016-7408 in Dropbear SSH
Summary
by MITRE
The dbclient in Dropbear SSH before 2016.74 allows remote attackers to execute arbitrary code via a crafted (1) -m or (2) -c argument.
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Analysis
by VulDB Data Team • 09/03/2020
The CVE-2016-7408 vulnerability represents a critical command injection flaw in the Dropbear SSH implementation that affects versions prior to 2016.74. This vulnerability specifically targets the dbclient component which is part of the Dropbear SSH suite commonly used in embedded systems and lightweight environments where full OpenSSH implementations are not feasible. The vulnerability stems from insufficient input validation and sanitization of command-line arguments, creating a pathway for remote attackers to inject malicious commands through the -m and -c parameters.
The technical flaw manifests in how the dbclient processes command-line arguments without proper sanitization or validation of user-supplied input. When attackers provide crafted arguments using the -m (message) or -c (command) flags, the system fails to properly escape or filter these inputs before executing them within the shell context. This allows for arbitrary command execution as the privileges of the user running the dbclient process, potentially escalating to root access if the client runs with elevated privileges. The vulnerability is particularly dangerous because it operates at the command-line argument parsing level, making it difficult to detect through standard network monitoring or firewall rules.
The operational impact of this vulnerability extends beyond simple remote code execution, as it can enable attackers to establish persistent access to systems running vulnerable versions of Dropbear SSH. Attackers can leverage this vulnerability to gain unauthorized access to network devices, embedded systems, and servers that rely on Dropbear for SSH connectivity. This is especially concerning in IoT environments and network appliances where Dropbear is commonly deployed and where patching cycles may be infrequent or difficult to implement. The vulnerability can be exploited remotely without authentication, making it particularly attractive to attackers seeking to compromise systems in the wild.
Mitigation strategies for CVE-2016-7408 primarily focus on immediate version upgrades to Dropbear 2016.74 or later, which includes proper input validation and sanitization for command-line arguments. Organizations should also implement network segmentation and access controls to limit exposure of systems running vulnerable versions. Additionally, monitoring for unusual command-line patterns and implementing intrusion detection systems can help identify exploitation attempts. The vulnerability aligns with CWE-78 which describes improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.001 for command and scripting interpreter. System administrators should also consider implementing mandatory access controls and privilege separation to limit the impact of successful exploitation, as the vulnerability can potentially lead to complete system compromise when executed with elevated privileges.