{"id":154530,"date":"2026-01-20T23:11:56","date_gmt":"2026-01-20T21:11:56","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-telnetd-pozvolyayushhaya-podklyuchitsya-s-pravami-root-bez-autentifikaczii"},"modified":"2026-01-20T23:11:56","modified_gmt":"2026-01-20T21:11:56","slug":"uyazvimost-v-telnetd-pozvolyayushhaya-podklyuchitsya-s-pravami-root-bez-autentifikaczii","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/uyazvimost-v-telnetd-pozvolyayushhaya-podklyuchitsya-s-pravami-root-bez-autentifikaczii","title":{"rendered":"A vulnerability in telnetd allows root access without authentication.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

A vulnerability has been identified in the telnetd server from the GNU InetUtils set, allowing connections as any user, including the root user, without password verification. A CVE identifier has not yet been assigned. The vulnerability has existed since InetUtils version 1.9.3 (2015) and remains unpatched in the current release 2.7.0. A fix is available in the form of patches (1, 2). <\/p>\n

The issue arises because the telnetd process calls the utility \"\/usr\/bin\/login\" for password verification, passing the username provided by the client upon connection as an argument to it. server<\/a>The \"login\" utility supports the \"-f\" option, which allows a user to log in without performing authentication (it's implied that this option is used when the user has already been verified). Thus, if you can inject the \"-f\" option into the username, you can connect without password verification. <\/p>\n

When connecting normally, using a username like \"-f root\" won't work, but telnet has an automatic connection mode that can be activated with the \"-a\" option. In this mode, the username is not taken from the command line but is passed through the USER environment variable. When the login utility is invoked, the value of this environment variable is inserted without additional checks and without escaping special characters. Therefore, to connect as the root user, it's sufficient to set the USER environment variable to \"-f root\" and connect to the telnet server with the \"-a\" option: $ USER='-f root' telnet -a server_name <\/p>\n

The change that led to the vulnerability was added to the telnetd code in March 2015 and was associated with addressing a problem that prevented identifying the username in autologin mode without authentication in Kerberos. As a solution, support was added for passing the username for autologin mode via an environment variable, but the verification of the correctness of the username from the environment variable was forgotten.
\n
Source: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0412 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 telnetd \u0438\u0437 \u043d\u0430\u0431\u043e\u0440\u0430 GNU InetUtils \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0430\u044f \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0438\u0442\u044c\u0441\u044f \u043f\u043e\u0434 \u043b\u044e\u0431\u044b\u043c \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c, \u0432\u043a\u043b\u044e\u0447\u0430\u044f \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044f root, \u0431\u0435\u0437 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0438 \u043f\u0430\u0440\u043e\u043b\u044f. 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