Authentication Bypass Vulnerability Affecting Telnetd
A critical vulnerability affecting Telnetd would allow a malicious actor to connect to affected systems by bypassing the authentication mechanism.
Description
Technical context and vulnerability details
Telnetd (Telnet daemon) is a service that allows users to remotely connect to a server or network equipment via the telnet communications protocol. This service is affected by a critical vulnerability labeled CVE-2026-24061 resulting from poor validation of the “USER” variable transmitted by the Telnet client during connection establishment. By sending the value “-f root” via the “USER” variable, a malicious actor could bypass the authentication mechanism and gain privileged access to the affected system. It is classified critical with a severity score of 9.8 according to CVSS V3.1.
Potential Risks & Impact
Potential consequences upon exploitation
- Bypassing the authentication mechanism;
- Unauthorized access to data;
- Data privacy breach;
- Compromise of system integrity;
Affected systems
Products, components and targeted versions
- GNU InetUtils telnetd version ranging from 1.9.3 to 2.7;
Recommended Remediations & Actions
Immediate actions and recommended mitigations
- update GNU InetUtils telnetd to the latest stable versions available;
- restrict access to port 23 so that it is only accessible from trusted IP addresses;
- permanently remove the telnetd service and replace it with SSH to secure and encrypt remote access;
Sources & External Links
Vendor security advisories and documentation
Advisory Specifications
CSIRT Emergency Response
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