# telnet exploit situation is crazy Source: https://www.youtube.com/watch?v=mdYDG34YP4w Recap page: https://rapidrecap.app/video/mdYDG34YP4w Generated: 2026-01-28T16:37:41.948+00:00 --- ## Quick Overview The critical authentication bypass vulnerability in GNU IneUtils TelnetD, CVE-2026-24061, allows attackers to gain root access by supplying a carefully crafted USER environment variable via the unencrypted Telnet protocol, which is easily exploitable using the -f flag in the login binary. **Key Points:** - Nearly 800,000 Telnet servers are exposed to remote attacks due to the unencrypted nature of Telnet and this specific vulnerability (CVE-2026-24061). - The flaw stems from the telnetd server's failure to sanitize the USER environment variable received from the client before passing it to login(1), which then uses the -f flag to bypass normal authentication. - The vulnerability affects GNU InetUtils versions 1.9.3 up to and including version 2.7, and was patched in version 2.8 (released January 20th). - The exploit is simple: send a crafted USER environment variable (e.g., 'USER=-f root') during the Telnet session negotiation to achieve root access. - Security researcher Kyu Neushwaistein (aka Carlos Cortes Alvarez) reported the flaw on January 19, 2026. - The existence of this vulnerability is concerning because Telnet transmits credentials in plain text, allowing attackers to easily sniff usernames and passwords. - The video sponsor, Tracebit, offers security canaries to detect such attacks instantly, demonstrating deployment of canaries for AWS credentials, SSH keys, and user/password logins. ![Screenshot at 00:05: The BleepingComputer article headline states "Nearly 800,000 Telnet servers exposed to remote attacks," setting the context for the discussion on the widespread risk posed by the Telnet vulnerability.](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-00-05.jpg) **Context:** The video discusses the security implications of a critical authentication bypass vulnerability, CVE-2026-24061, found in the GNU IneUtils TelnetD service. Telnet, an old protocol, is inherently insecure as it sends data in plain text. The speaker reviews an article detailing that nearly 800,000 servers still use this protocol, making them susceptible to this specific exploit which allows unauthenticated root access. ## Detailed Analysis The video analyzes a critical vulnerability (CVE-2026-24061) affecting GNU InetUtils TelnetD, which allows remote, unauthenticated root access. The vulnerability exists because the telnetd server does not properly sanitize the USER environment variable passed to the login binary. If an attacker supplies a carefully crafted USER environment value, such as 'USER=-f root', the login process automatically logs them in as root, bypassing normal authentication. This exploit works because the telnet process uses the -f flag to skip authentication when processing user input from the environment. The affected versions range from 1.9.3 up to 2.7, with a patch released in version 2.8 on January 20th. The speaker demonstrates the exploit by running a proof-of-concept tool, successfully achieving root access (UID 0) after connecting to a local Telnet instance configured to be vulnerable. Furthermore, the speaker highlights that because Telnet transmits data in clear text, attackers can easily sniff credentials used on vulnerable systems. The video also features a sponsorship segment for Tracebit, a security monitoring tool that deploys 'canaries' (fake credentials/data) to detect when attackers attempt to use stolen credentials, such as the SSH key canary used to prove the detection capability. ### Telnet Vulnerability Overview - Nearly 800,000 exposed servers rely on the insecure Telnet protocol - The specific flaw CVE-2026-24061 allows authentication bypass to root - Affects GNU InetUtils versions 1.9.3 through 2.7; patched in 2.8. ### Exploitation Mechanism - The telnetd server passes an unsanitized USER environment variable to login(1) - Using the -f flag allows login as root by bypassing authentication - The exploit is as simple as echoing 'USER=-f root' into the Telnet session. ### Demonstration - Speaker installs Tracebit CLI - Authenticates to Tracebit server - Deploys all canary types (AWS, SSH, Cookie, etc.) - Triggers the SSH canary using the exploit command to confirm detection - Successfully gains root access (UID 0) on the vulnerable instance. ### Threat Intelligence Context - GreyNoise observed exploitation attempts immediately after the patch release - The vulnerability is dangerous because Telnet traffic is plaintext, exposing credentials. ### Sponsor Promotion (Tracebit) - Tracebit offers security canaries to detect credential theft instantly - Community Edition is free, offering 5 of each canary type (AWS, SSH, Cookie, Email/Password) - Enterprise offers advanced coverage like cloud infrastructure and Kubernetes canaries. ![Screenshot at 00:05: The BleepingComputer article headline states "Nearly 800,000 Telnet servers exposed to remote attacks," setting the context for the discussion on the widespread risk posed by the Telnet vulnerability.](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-00-05.jpg) ![Screenshot at 00:48: The headline highlights the scale of the problem: "Nearly 800,000 Telnet servers exposed to remote attacks."](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-00-48.jpg) ![Screenshot at 02:05: The Tracebit CLI installation script runs, showing the download and successful installation of the Tracebit CLI tool.](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-02-05.jpg) ![Screenshot at 03:54: The speaker shows a Kali Linux terminal environment where the Proof of Concept \(PoC\) exploit tool is ready to run.](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-03-54.jpg) ![Screenshot at 05:27: The speaker reviews the Git commit history on Codeberg showing the exact lines of code in telnetd.c where the vulnerability was introduced in 2015.](https://ss.rapidrecap.app/screens/mdYDG34YP4w/00-05-27.jpg)