Source: cve@mitre.org
Vulnerability in SMI Sendmail 4.0 and earlier, on SunOS up to 4.0.3, allows remote attackers to access user bin.
Critical vulnerability in Sendmail versions 4.0 and earlier on SunOS systems allows for remote unauthorized access to the bin directory, potentially enabling attackers to execute arbitrary commands with elevated privileges. This flaw poses a significant risk of system compromise and data exfiltration due to the ability to gain control of the target system.
Step 1: Target Identification: The attacker identifies a vulnerable Sendmail server running on SunOS 4.0.3 or earlier. This can be achieved through port scanning (port 25) and banner grabbing.
Step 2: Malformed Request Creation: The attacker crafts a malicious request (e.g., a specially crafted email or command) designed to exploit the vulnerability. The specific payload depends on the exact nature of the flaw (e.g., format string, buffer overflow). The request is sent to the Sendmail server.
Step 3: Vulnerability Trigger: The Sendmail server processes the malicious request. Due to the lack of proper input validation, the crafted input triggers the vulnerability, leading to memory corruption or code execution.
Step 4: Code Execution: The attacker's payload (e.g., shellcode) is executed with the privileges of the Sendmail process. This allows the attacker to gain control of the system.
Step 5: Privilege Escalation (Potential): The attacker might leverage the access to the bin directory to execute commands or install backdoors, further escalating their privileges and gaining persistent access.
The vulnerability stems from a flaw in how Sendmail handled requests, specifically related to the processing of certain commands or parameters. The exact mechanism isn't explicitly detailed in the CVE, but it's likely related to a format string vulnerability, a buffer overflow, or an unchecked input validation issue. Older versions of Sendmail, particularly those on SunOS 4.0.3 and earlier, lacked robust input sanitization. This allowed attackers to craft malicious requests that could overwrite critical memory locations, leading to the execution of arbitrary code with the privileges of the Sendmail process (typically root). The ability to access the bin directory suggests the attacker could potentially leverage existing binaries within that directory to escalate privileges or install backdoors.
This vulnerability is a prime target for opportunistic attackers and could be leveraged by various threat actors. While specific APT groups aren't directly linked to this CVE, the ease of exploitation and potential for system compromise make it attractive. The vulnerability is not listed on the CISA KEV list due to its age and the limited number of affected systems.
Network traffic analysis: Look for unusual SMTP traffic, especially malformed or unusually long email headers or body content. Analyze SMTP logs for suspicious commands or activity.
File integrity monitoring: Monitor the bin directory for unexpected changes, new files, or modifications to existing binaries.
System log analysis: Review system logs (e.g., syslog) for errors or unusual activity related to Sendmail or other system processes.
Honeypots: Deploying a Sendmail honeypot can help detect and analyze exploitation attempts.
Upgrade Sendmail: The primary remediation is to upgrade to a patched version of Sendmail. This is the most effective solution.
Operating System Patching: Ensure the underlying SunOS system is patched with all relevant security updates.
Network Segmentation: Isolate vulnerable systems from the rest of the network to limit the impact of a successful exploit.
Intrusion Detection/Prevention Systems (IDS/IPS): Deploy and configure IDS/IPS to detect and block malicious traffic targeting Sendmail.
Least Privilege: Ensure that the Sendmail process runs with the least necessary privileges.
Regular Security Audits: Conduct regular security audits and penetration testing to identify and address vulnerabilities.