Critical Unpatched Telnetd Flaw (CVE-2026-32746) Enables Unauthenticated Root RCE via Port 23
Critical Unpatched Telnetd Flaw (CVE-2026-32746) Enables Unauthenticated Root RCE via Port 23
Cybersecurity researchers have disclosed a critical security flaw impacting the GNU InetUtils telnet daemon (telnetd) that could be exploited by an unauthenticated remote attacker to execute arbitrary code with elevated privileges.
The vulnerability, tracked as CVE-2026-32746, carries a CVSS score of 9.8 out of 10.0. It has been described as a case of out-of-bounds write in the LINEMODE Set Local Characters (SLC) suboption handler that results in a buffer overflow, ultimately paving the way for code execution.
Israeli cybersecurity company Dream, which discovered and reported the flaw on March 11, 2026, said it affects all versions of the Telnet service implementation through 2.7. A fix for the vulnerability is expected to be available no later than April 1, 2026.
“An unauthenticated remote attacker can exploit this by sending a specially crafted message during the initial connection handshake — before any login prompt appears,” Dream said in an alert. “Successful exploitation can result in remote code execution as root.”
“A single network connection to port 23 is sufficient to trigger the vulnerability. No credentials, no user interaction, and no special network position are required.”
The SLC handler, per Dream, processes option negotiation during the Telnet protocol handshake. But given that the flaw can be triggered before authentication, an attacker can weaponize it immediately after establishing a connection by sending specially crafted protocol messages.
Successful exploitation could result in complete system compromise if telnetd runs with root privileges. This, in turn, could open the door to various post-exploitation actions, including the deployment of persistent backdoors, data exfiltration, and lateral movement by using the compromised hosts as pivot points.
“An unauthenticated attacker can trigger it by connecting to port 23 and sending a crafted SLC suboption with many triplets,” according to Dream security researcher Adiel Sol.
“No login is required; the bug is hit during option negotiation, before the login prompt. The overflow corrupts memory and can be turned into arbitrary writes. In practice, this can lead to remote code execution. Because telnetd usually runs as root (e.g., under inetd or xinetd), a successful exploit would give the attacker full control of the system.”
In the absence of a fix, it’s advised to disable the service if it’s not necessary, run telnetd without root privileges where required, block port 23 at the network perimeter and host-based firewall level to restrict access, and isolate Telnet access.
The disclosure comes nearly two months after another critical security flaw was disclosed in GNU InetUtils telnetd (CVE-2026-24061, CVSS score: 9.8) that could be leveraged to gain root access to a target system. The vulnerability has since come under active exploitation in the wild, per the U.S. Cybersecurity and Infrastructure Security Agency.
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