Source: cve@mitre.org
Vulnerability in in.telnetd in SunOS 4.1.1 and earlier allows local users to gain root privileges.
SunOS 4.1.1 and earlier systems are critically vulnerable to a local root privilege escalation via a flaw in the in.telnetd service. This allows attackers to gain complete control of the system. This vulnerability, dating back to 1991, poses a significant risk to any legacy systems still in operation.
Step 1: Establish Telnet Connection: The attacker initiates a Telnet connection to the vulnerable SunOS system.
Step 2: Trigger Vulnerability: The attacker sends a specially crafted input to in.telnetd. This input is designed to exploit the memory corruption vulnerability.
Step 3: Memory Corruption: The crafted input overflows a buffer or corrupts other memory structures within the in.telnetd process.
Step 4: Code Execution Hijack: The memory corruption overwrites a critical memory location, such as the return address of a function. The attacker controls the new return address.
Step 5: Shellcode Execution: The attacker's crafted input includes shellcode (or a pointer to shellcode) that is executed when the function returns. This shellcode typically executes a command to escalate privileges.
Step 6: Privilege Escalation: The shellcode executes a command to obtain root privileges, such as setting the effective user ID to 0 or executing a setuid program.
The vulnerability lies within the in.telnetd service's handling of user authentication or session management. The exact mechanism is likely a buffer overflow or a similar memory corruption issue. The service likely fails to properly validate input, allowing an attacker to overwrite critical memory regions, potentially including the stack or heap. This overwrite could then be leveraged to overwrite the return address of a function, redirecting execution to attacker-controlled code, and ultimately executing commands with root privileges. The age of the vulnerability suggests a lack of modern security mitigations like ASLR or DEP, making exploitation easier.
Due to the age of the vulnerability, it's unlikely to be actively targeted by sophisticated APT groups. However, it could be exploited by less sophisticated actors or used as part of a larger attack chain. The vulnerability is not listed on the CISA KEV catalog due to its age and the rarity of vulnerable systems.
Monitor network traffic for Telnet connections to the affected systems.
Analyze system logs for suspicious activity related to in.telnetd, such as unexpected errors or crashes.
Examine core dumps or memory dumps of in.telnetd for signs of memory corruption.
Use intrusion detection systems (IDS) with signatures for known exploits of this vulnerability.
Monitor for the creation of unexpected setuid binaries or changes to root-owned files.
Isolate Affected Systems: Immediately isolate any systems running SunOS 4.1.1 or earlier from the network.
Upgrade or Migrate: The primary remediation is to upgrade to a supported and patched version of SunOS or migrate to a modern operating system. This is the most effective solution.
Disable Telnet: If upgrading is not immediately possible, disable the telnetd service. This will prevent exploitation of the vulnerability.
Implement Network Segmentation: If telnetd must remain enabled for legitimate purposes, segment the network to limit access to the vulnerable systems.
Apply Security Patches (If Available): While patches for such old systems are unlikely, check for any available security patches or workarounds from the vendor or community.
Regular Security Audits: Conduct regular security audits and penetration tests to identify and address vulnerabilities.