Privilege Escalation in Exim via .forward Misconfiguration

Executive Summary

Exim before version 4.99.5 has a vulnerability where the .forward file feature can be exploited for privilege escalation. This happens because the force_command setting in a pipe transport is not handled correctly, allowing an attacker to execute arbitrary commands with elevated privileges.

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Detection Guidance

To detect this vulnerability, check the Exim version installed on your system. Run: exim --version. If the version is below 4.99.5, the system is vulnerable. Additionally, review .forward files in user directories for suspicious commands or paths that could lead to privilege escalation.

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Impact Analysis

If you use Exim versions before 4.99.5, an attacker with local access could escalate their privileges to gain full control over the system. This could lead to unauthorized data access, system compromise, or further network infiltration.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR's data protection requirements and HIPAA's security rules. Organizations using vulnerable Exim versions may face compliance violations, legal penalties, and reputational damage.

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Mitigation Strategies

Upgrade Exim to version 4.99.5 or later to address the .forward privilege escalation issue.

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