Source: cve@mitre.org
SunOS sendmail 5.59 through 5.65 uses popen to process a forwarding host argument, which allows local users to gain root privileges by modifying the IFS (Internal Field Separator) variable and passing crafted values to the -oR option.
SunOS sendmail versions 5.59 through 5.65 are vulnerable to a local root privilege escalation. By manipulating the IFS environment variable and the -oR option, attackers can execute arbitrary commands with root privileges, potentially leading to complete system compromise.
Step 1: Environment Variable Manipulation: The attacker sets the IFS (Internal Field Separator) environment variable to a value that allows for bypassing standard command parsing, such as a space or tab. This is crucial for injecting commands into the -oR argument.
Step 2: Crafted -oR Argument: The attacker crafts a malicious forwarding host argument to the -oR option. This argument contains shell commands designed to execute arbitrary code. The commands are designed to be executed with root privileges.
Step 3: Sendmail Execution: The attacker sends an email or uses a sendmail command-line interface to trigger the vulnerable code path. The crafted -oR argument is passed to sendmail.
Step 4: popen() Execution: Sendmail uses popen() to execute the forwarding host argument. Because the IFS variable is modified and the input is not sanitized, the attacker's shell commands are executed.
Step 5: Privilege Escalation: The attacker's injected commands are executed with root privileges, granting the attacker full control over the system.
The vulnerability stems from the insecure use of popen() within sendmail to process the forwarding host argument provided via the -oR option. The program fails to properly sanitize the input, allowing attackers to inject shell commands. By modifying the IFS environment variable, attackers can bypass standard command parsing and execute malicious code. Specifically, the lack of input validation on the forwarding host argument allows for command injection. The popen() function is then used to execute the attacker-controlled command, granting root privileges due to sendmail's elevated permissions. The root cause is a command injection vulnerability due to insufficient input validation and the use of popen() to execute user-controlled input.
Due to the age of the vulnerability, specific APT groups are unlikely to be actively targeting this. However, it is possible that older, less sophisticated threat actors may still attempt to exploit this vulnerability on legacy systems. CISA KEV status is not applicable due to the age of the vulnerability.
Monitor sendmail logs for suspicious activity, such as unusual command-line arguments passed to the -oR option.
Analyze email headers for unusual forwarding host entries.
Inspect system logs for unexpected processes spawned by sendmail with root privileges.
Monitor for changes to the IFS environment variable, especially if sendmail is running.
Network traffic analysis for sendmail related traffic, looking for unusual command injection attempts.
Upgrade to a patched version of sendmail (e.g., version 8.x or later).
Implement input validation to sanitize all arguments passed to sendmail, especially those related to forwarding hosts.
Restrict the use of the -oR option if possible.
Apply the principle of least privilege: ensure sendmail runs with the minimum necessary privileges.
Regularly update and patch all software on the system.
Implement a host-based intrusion detection system (HIDS) to monitor for suspicious activity.
Consider using a more secure mail transfer agent (MTA) if possible.