libssh Memory Leak via Malicious SFTP Server Responses

Executive Summary

This is a denial of service vulnerability in libssh affecting its client-side SFTP message handling. A malicious SFTP server can send responses for unknown request IDs that libssh clients keep queued indefinitely, causing unbounded memory growth and client-side denial of service.

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Detection Guidance

Monitor memory usage on systems using libssh for SFTP connections. Check for unusual accumulation of queued SFTP messages by inspecting network traffic for repeated responses with unknown request IDs. Use tools like tcpdump or Wireshark to capture and analyze SFTP traffic for anomalies.

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Impact Analysis

If you use a vulnerable libssh client to connect to an untrusted SFTP server, the server could exploit this flaw to consume excessive memory on your system. This may lead to system slowdowns, crashes, or complete denial of service for applications relying on libssh.

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Compliance Impact

This vulnerability primarily causes a denial of service by consuming excessive memory on the client side, which could disrupt services handling sensitive data. While not directly violating GDPR or HIPAA, prolonged downtime could impact data availability and processing timelines, potentially affecting compliance with data protection and security requirements.

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Mitigation Strategies

Update libssh to the latest patched version. Avoid connecting to untrusted SFTP servers. Implement network-level monitoring to detect and block malicious SFTP traffic patterns. Restrict SFTP access to trusted servers only.

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