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How CVE-2023-28303 works:
The vulnerability resides in the telnet daemon (telnetd) of GNU Inetutils, affecting versions up to 2.7. During telnet authentication, the daemon uses the USER environment variable to identify the connecting user. However, improper input validation allows an attacker to set the USER variable to “-f root”. This string is misinterpreted by the authentication logic as a command-line argument. The “-f” flag typically instructs the system to skip password verification or specify a user, and when combined with “root”, it bypasses all authentication checks. The telnetd service fails to sanitize or validate the USER variable, leading to argument injection. This flaw enables remote attackers to manipulate the authentication process by crafting a malicious telnet request. By sending a connection with USER=”-f root”, the daemon grants unauthorized access as the root user without requiring a password. Exploitation occurs over the network without any prior credentials, leveraging the insecure parsing of environment variables in the telnetd source code. The vulnerability allows full system compromise, as attackers gain elevated privileges directly. This issue highlights the risks of trusting user-supplied input without rigorous validation in network services.
Platform: GNU Inetutils
Version: Through 2.7
Vulnerability: Authentication bypass
Severity: Critical
Date: 2023-05-22
Prediction: Patch 2023-05-22
What Undercode Say:
Analytics:
export USER=”-f root”
telnet target_host
nc -v target_host 23
strings telnetd | grep auth
ps aux | grep telnetd
How Exploit:
Set USER environment variable to “-f root” during telnet connection. Remote attackers send crafted packets to bypass authentication, gaining root access without credentials. Exploit requires network access to telnetd port.
Protection from this CVE:
Update GNU Inetutils.
Disable telnetd service.
Use network segmentation.
Implement input validation.
Impact:
Remote root access.
Full system compromise.
Authentication bypass.
Critical severity impact.
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Sources:
Reported By: www.cve.org
Extra Source Hub:
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