CVE-2016-7409 in Dropbear SSH
Summary
by MITRE
The dbclient and server in Dropbear SSH before 2016.74, when compiled with DEBUG_TRACE, allows local users to read process memory via the -v argument, related to a failed remote ident.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2016-7409 affects the Dropbear SSH implementation, specifically impacting both client and server components when compiled with the DEBUG_TRACE flag enabled. This flaw represents a significant information disclosure issue that can be exploited by local users to gain unauthorized access to process memory contents through the verbose command-line argument. The vulnerability stems from insufficient input validation and memory handling within the SSH protocol implementation, particularly when the debug tracing functionality is active during program execution. The issue is particularly concerning because it allows attackers to extract sensitive information from memory locations that should remain protected, potentially exposing cryptographic keys, session data, or other confidential information processed by the SSH daemon.
The technical root cause of this vulnerability lies in the improper handling of the -v argument when DEBUG_TRACE is enabled, which creates a pathway for memory disclosure through failed remote ident operations. When the debug trace functionality is active, the application fails to properly sanitize or validate the verbose argument input, allowing malicious local users to craft specific inputs that trigger memory read operations. This weakness is categorized under CWE-200, Information Exposure, and specifically relates to improper handling of debugging features that should never be accessible in production environments. The vulnerability demonstrates a classic case of insufficient input validation where user-controllable data is directly processed without proper bounds checking or memory access restrictions, creating an information leak that can be exploited to extract sensitive data from the process address space.
The operational impact of CVE-2016-7409 extends beyond simple information disclosure, as it can provide attackers with access to cryptographic material and session information that could be used for further exploitation. Local users who can execute the -v argument against a vulnerable Dropbear SSH implementation can potentially extract session keys, user credentials, or other sensitive data that would normally be protected in memory. This vulnerability aligns with ATT&CK technique T1005, Data from Local System, and can be leveraged as a stepping stone for more sophisticated attacks. The risk is particularly elevated in environments where Dropbear SSH is compiled with debugging features enabled in production systems, which violates security best practices and creates unnecessary attack surface. The vulnerability can be exploited even without network connectivity, as it relies solely on local process manipulation, making it particularly dangerous in multi-tenant or shared hosting environments.
Mitigation strategies for CVE-2016-7409 focus primarily on ensuring that Dropbear SSH implementations do not compile with DEBUG_TRACE enabled in production environments. System administrators should immediately update to Dropbear SSH version 2016.74 or later, which contains the necessary patches to address this vulnerability. Organizations should implement strict build policies that disable debugging features in production deployments and conduct regular security audits to ensure that development flags are not inadvertently enabled in operational systems. The vulnerability also highlights the importance of following secure coding practices and avoiding the inclusion of debug functionality in production builds, as outlined in the OWASP Secure Coding Practices. Additionally, monitoring for unusual process memory access patterns and implementing proper access controls can help detect potential exploitation attempts, though the most effective mitigation remains the immediate patching of affected systems and the removal of debug flags from production deployments.