Source: cve@mitre.org
Vulnerability in rcp on SunOS 4.0.x allows remote attackers from trusted hosts to execute arbitrary commands as root, possibly related to the configuration of the nobody user.
**SunOS 4.0.x's rcp (remote copy) utility suffers from a critical vulnerability allowing remote attackers from trusted hosts to gain root-level access. This flaw, stemming from improper handling of user privileges, enables attackers to execute arbitrary commands on the vulnerable system, potentially leading to complete system compromise and data exfiltration.
Step 1: Trust Establishment: The attacker must originate from a host listed in the .rhosts file on the target SunOS 4.0.x system. This file defines which remote hosts are considered 'trusted'.
Step 2: rcp Invocation: The attacker uses the rcp command to copy a malicious file or command to the target system. This command is executed from the trusted host.
Step 3: Authentication Bypass: The rcp utility, due to the trust relationship, bypasses standard authentication mechanisms. It relies on the source IP address and hostname for authorization.
Step 4: Command Execution: The attacker's malicious command, potentially disguised as a file, is executed on the target system with the privileges of the user that initiated the rcp command (which, due to the .rhosts configuration, can be root or a user with root-level access). This is often achieved by exploiting the configuration of the nobody user or other system-level vulnerabilities.
Step 5: Privilege Escalation: The attacker leverages the lack of proper authentication and authorization to execute commands with elevated privileges, potentially gaining root access.
The vulnerability lies within the rcp implementation on SunOS 4.0.x, specifically related to how it handles user authentication and privilege escalation. The flaw stems from a combination of factors, including the reliance on the .rhosts file for trust relationships and the potential for misconfiguration of the nobody user. The rcp utility, when invoked from a trusted host (as defined by .rhosts), doesn't adequately validate the user's identity or permissions, allowing for the execution of commands with elevated privileges. This is exacerbated by the fact that the nobody user may be configured in a way that allows it to execute commands as root under certain circumstances. The root cause is a privilege escalation vulnerability due to insufficient input validation and improper handling of user context during remote copy operations. It's not a buffer overflow or race condition in the traditional sense, but rather a design flaw in the trust model and privilege delegation.
Due to the age of the vulnerability, it's unlikely to be directly associated with specific modern APT groups. However, any threat actor targeting legacy systems would likely leverage this vulnerability. This vulnerability is not listed in the CISA KEV catalog due to its age and the limited number of active deployments.
Monitor network traffic for rcp commands originating from unexpected or untrusted hosts.
Analyze system logs (e.g., /var/log/syslog) for suspicious rcp activity, especially those involving the creation or modification of system files or the execution of unusual commands.
Review .rhosts files for unauthorized entries or misconfigurations.
Implement file integrity monitoring to detect changes to critical system files.
Network Intrusion Detection Systems (NIDS) can be configured to detect anomalous rcp traffic patterns, especially if they involve the transfer of executable files.
Isolate or decommission affected systems immediately. This is the most effective mitigation strategy.
Remove or disable the rcp service. Replace it with more secure alternatives like scp (Secure Copy) or rsync over SSH.
Review and remove all .rhosts files. These files are inherently insecure and should not be used.
Implement strong authentication mechanisms such as SSH key-based authentication for remote access.
Patch or upgrade to a supported operating system. SunOS 4.0.x is no longer supported and should be replaced.
Implement a host-based firewall to restrict network access to the system.
Regularly audit system configurations for security vulnerabilities.