Source: cve@mitre.org
Local users can start Sendmail in daemon mode and gain root privileges.
Sendmail, a widely used email server, is vulnerable to a local privilege escalation. Attackers can leverage this flaw to gain root access, allowing them to completely compromise the affected system and potentially exfiltrate sensitive data or disrupt operations. This vulnerability poses a significant risk to systems running vulnerable versions of Sendmail.
Step 1: Local Access: The attacker must first have local access to the vulnerable system, typically through a compromised user account or physical access. Step 2: Crafting the Payload: The attacker crafts a malicious command-line argument designed to exploit the Sendmail vulnerability. This argument will likely contain a carefully constructed payload, such as shellcode, designed to execute arbitrary commands. Step 3: Triggering the Vulnerability: The attacker executes a command to start Sendmail in daemon mode, passing the crafted malicious argument. This can be done directly or indirectly through other applications that interact with Sendmail. Step 4: Code Execution: Sendmail processes the malicious argument, triggering the buffer overflow or other memory corruption. The attacker's injected code is then executed with the privileges of the Sendmail daemon, which is typically root. Step 5: Privilege Escalation: The attacker's code executes, granting the attacker root privileges and full control over the system.
The vulnerability stems from a design flaw in Sendmail's handling of command-line arguments when starting in daemon mode. Specifically, the program doesn't adequately sanitize user-supplied input. By crafting a malicious command-line argument, a local user can trigger a buffer overflow or other memory corruption issues. This allows the attacker to overwrite critical memory regions, such as the stack, and inject malicious code. The injected code, when executed with root privileges, grants the attacker complete control over the system. The root cause is a lack of input validation and improper handling of user-controlled data passed to the Sendmail daemon.
Due to the age and nature of the vulnerability, it's likely exploited by a wide range of actors, from script kiddies to sophisticated threat actors. It's difficult to attribute specific APT groups with certainty, but any group seeking to maintain persistence or gain access to a system would likely leverage this vulnerability if present. This vulnerability is not listed on the CISA KEV.
Monitor system logs (e.g., /var/log/syslog, /var/log/messages) for suspicious Sendmail activity, such as unexpected command-line arguments or errors.
Analyze process execution history for unusual Sendmail invocations.
Implement file integrity monitoring to detect changes to Sendmail binaries or configuration files.
Network traffic analysis: Look for unusual network connections originating from the Sendmail process, especially to external hosts.
Use intrusion detection/prevention systems (IDS/IPS) with signatures for known Sendmail exploits.
Upgrade Sendmail to the latest version or a version that addresses the vulnerability. This is the most effective mitigation.
Apply security patches provided by the vendor.
Restrict local user access and privileges to minimize the attack surface.
Implement strong input validation to prevent malicious command-line arguments from being passed to Sendmail.
Regularly audit system logs and security configurations.
Consider using a web application firewall (WAF) to filter malicious traffic.