Source: cve@mitre.org
The debug command in Sendmail is enabled, allowing attackers to execute commands as root.
Critical vulnerability in Sendmail versions with the debug command enabled allows for unauthenticated remote root code execution. Successful exploitation grants attackers complete control over the compromised system, potentially leading to data breaches, system compromise, and denial-of-service. This vulnerability is extremely dangerous due to its potential for widespread impact.
Step 1: Identify Target: The attacker identifies a target system running a vulnerable version of Sendmail with the debug command enabled. This can be achieved through port scanning (e.g., port 25) and banner grabbing.
Step 2: Establish Connection: The attacker establishes a connection to the Sendmail service, typically via SMTP (port 25).
Step 3: Trigger Debug Mode: The attacker sends a specific command or series of commands to Sendmail to activate the debug mode. The exact command sequence may vary depending on the Sendmail version.
Step 4: Command Injection: The attacker crafts a malicious command designed to be executed by the Sendmail process. This command is injected through the debug interface.
Step 5: Code Execution: The Sendmail daemon, running with root privileges, executes the attacker-supplied command. This could involve creating a reverse shell, installing a backdoor, or modifying system files.
Step 6: System Compromise: The attacker gains complete control over the compromised system.
The vulnerability stems from the Sendmail daemon's debug command functionality. This command, when enabled, provides privileged access to the underlying system. The root cause is a lack of proper input validation and access control for the debug command. Specifically, attackers can craft malicious commands that are then executed with root privileges. This bypasses normal security checks and allows for arbitrary code execution. The flaw lies in the insecure handling of user-supplied input passed to the debug command, leading to a direct execution of attacker-controlled commands.
This vulnerability is a classic example of a critical remote code execution flaw. While specific APT groups may not be explicitly known to target this specific CVE, any attacker seeking to gain initial access or escalate privileges would find this vulnerability highly valuable. The age of the vulnerability makes it a likely target for opportunistic attacks. CISA KEV: Not listed.
Monitor SMTP traffic for unusual command sequences or debug commands. Specifically, look for commands that enable debug mode followed by suspicious activity.
Analyze Sendmail logs for suspicious activity, such as unexpected process executions or file modifications. Examine the logs for any instances of the debug command being used.
Implement network intrusion detection systems (IDS) with rules specifically designed to detect exploitation attempts against Sendmail's debug command.
Monitor system process activity for unexpected processes spawned by the Sendmail daemon.
Review system configuration files for the debug command being enabled. This includes checking the sendmail.cf file.
Disable the debug command in Sendmail if it is not required. This is the most effective mitigation.
Upgrade Sendmail to the latest version. Newer versions may have addressed this vulnerability or have improved security configurations.
Apply security patches provided by the vendor.
Implement a strong firewall configuration to restrict access to the Sendmail service (port 25) from untrusted networks.
Regularly audit Sendmail configuration files for any unauthorized changes.
Implement a host-based intrusion detection system (HIDS) to monitor for malicious activity on the system.
Enforce least privilege principles, ensuring that Sendmail runs with the minimum necessary privileges.