Denial of Service in Open-Xchange ManageSieve

Executive Summary

This vulnerability allows an unauthenticated attacker to crash the ManageSieve login process by sending a small malformed command before authenticating. In high-security mode, only the attacker's connection is affected, but in high-performance mode, all connections handled by the same process are terminated, leading to a denial of service for Sieve script management.

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Detection Guidance

Monitor ManageSieve service logs for repeated crashes or malformed command errors. Check for sudden termination of managesieve-login processes. Use network traffic analysis tools to detect unusual small malformed commands sent to the ManageSieve port before authentication.

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Impact Analysis

The impact depends on the mode: in high-security mode, only the attacker's connection is disrupted, but in high-performance mode, all users relying on the same ManageSieve process may lose access to Sieve script management, causing service disruption.

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Compliance Impact

This vulnerability could impact compliance with GDPR or HIPAA by enabling denial-of-service attacks on Sieve script management, potentially disrupting access to critical email filtering or storage systems. If exploited repeatedly, it may lead to service unavailability, violating availability requirements in these regulations.

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Mitigation Strategies

Restrict network access to the ManageSieve service to trusted clients only. Update to a non-vulnerable version of ManageSieve immediately. If immediate update is not possible, consider disabling the ManageSieve service until patched.

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