Source: cve@mitre.org
rdist in various UNIX systems uses popen to execute sendmail, which allows local users to gain root privileges by modifying the IFS (Internal Field Separator) variable.
Local privilege escalation is possible on vulnerable UNIX systems due to a flaw in the rdist utility's interaction with sendmail. By manipulating the IFS (Internal Field Separator) environment variable, attackers can inject arbitrary commands, leading to root access and complete system compromise.
Step 1: Environment Variable Manipulation: The attacker sets the IFS environment variable to a malicious value. This value is designed to allow command injection when rdist calls sendmail.
Step 2: Triggering rdist: The attacker triggers the rdist command, typically by creating or modifying files that are managed by rdist.
Step 3: popen() Execution: rdist calls popen() to execute sendmail to send a notification. The attacker-controlled IFS variable is passed to sendmail through the environment.
Step 4: Command Injection: Due to the modified IFS, the attacker's injected commands are interpreted by the shell, leading to the execution of arbitrary commands.
Step 5: Privilege Escalation: The injected commands are executed with the privileges of the user running rdist, which is often root, granting the attacker elevated access.
The vulnerability stems from the insecure use of popen() within the rdist utility when interacting with sendmail. rdist uses popen() to execute sendmail to send email notifications. The rdist program does not properly sanitize or escape the environment variables passed to sendmail. Specifically, the IFS variable, which controls how the shell parses command arguments, can be maliciously modified. By setting IFS to a specific value, an attacker can inject shell commands into the arguments passed to sendmail. This allows the attacker to execute arbitrary commands with the privileges of the user running rdist, which is often root when used for system administration tasks. The core issue is a lack of input validation and proper escaping of environment variables before they are passed to a shell command executed via popen(). This allows for command injection.
While no specific APTs are directly linked to this CVE, it is a common technique that could be used by any attacker. This is a low-hanging fruit vulnerability that is often exploited in initial access. This vulnerability is not listed in the CISA KEV database, likely due to its age and the focus on more modern threats.
Monitor system logs for unusual rdist activity, especially related to file modifications or distribution events.
Analyze process execution logs for suspicious invocations of sendmail with unusual environment variables, particularly IFS.
Implement file integrity monitoring to detect unauthorized changes to system files.
Network monitoring for unusual email traffic originating from the affected server, especially if it contains command execution indicators.
Apply security patches for the affected operating systems and rdist implementations.
Upgrade to modern versions of rdist or consider alternative file distribution tools.
Implement input validation and sanitization to prevent command injection vulnerabilities in all applications that interact with the shell.
Restrict the privileges of the user running rdist to the minimum necessary.
Disable or restrict the use of rdist if it is not required.
Review and harden the configuration of sendmail to prevent unauthorized email relaying or command execution.