Command Injection in Ruby Net::IMAP

Executive Summary

This vulnerability exists in the Net::IMAP library, which implements IMAP client functionality in Ruby. Before versions 0.6.5 and 0.5.15, some Net::IMAP commands accept a raw string argument that is only checked to prevent CRLF injection but is otherwise sent exactly as provided.

If this raw string comes from user input, an attacker can manipulate it so that the next IMAP command is treated as a continuation of the first command. This causes the first command to fail eventually but also blocks it from returning a response until another command is sent from a different thread.

The other command will then not return until the connection is closed, effectively causing a denial of service or blocking behavior. This issue was fixed in versions 0.6.5 and 0.5.15 of Net::IMAP.

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Impact Analysis

This vulnerability can impact you by causing IMAP commands to hang or block indefinitely, leading to denial of service conditions in applications using vulnerable versions of Net::IMAP.

An attacker who can supply user-controlled input to these commands can exploit this behavior to disrupt normal IMAP client operations, potentially affecting email retrieval or processing.

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Mitigation Strategies

To mitigate this vulnerability, update the Net::IMAP library to version 0.6.5 or later, or 0.5.15 or later, where the issue has been fixed.

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Compliance Impact

This vulnerability primarily causes denial of service conditions by allowing an attacker to manipulate command parsing, leading to command failure and hanging threads. It does not directly impact confidentiality or integrity of data.

Since the vulnerability does not result in unauthorized data access or data leakage, its impact on compliance with standards like GDPR or HIPAA—which focus heavily on protecting personal data confidentiality and integrity—is limited.

However, the potential availability issues caused by denial of service could indirectly affect compliance if critical services become unavailable, as availability is a component of many security frameworks.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual IMAP client behavior such as commands that hang or do not return promptly, especially in multi-threaded environments where one command waits indefinitely for another thread's command to complete.

Specifically, detection involves checking for Net::IMAP commands that include raw string arguments ending with "}" or patterns like "{0}" or "{0+}", which are known to bypass validation and cause the issue.

To detect this on your system, you can capture and analyze IMAP traffic for such suspicious command patterns.

• Use network packet capture tools like tcpdump or Wireshark to capture IMAP traffic on port 143 or 993.
• Filter captured traffic for IMAP commands containing raw string arguments ending with "}" or "{0}" or "{0+}".
• Example tcpdump command to capture IMAP traffic: tcpdump -i <interface> port 143 or port 993 -w imap_traffic.pcap
• Analyze the capture file with Wireshark or tshark to filter IMAP commands with suspicious patterns.
• If you have access to the Ruby environment, check the version of the ruby/net-imap gem to ensure it is updated to 0.6.5 or 0.5.15 or later, as these versions contain the fix.

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