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Linux Telnet Authentication Bypass

Detects an authentication bypass in telnet tracked as CVE-2026-24061. An attacker can supply a specifically crafted USER environment variable (-f root) that is passed to /usr/bin/login. Because this input isn't…

Description

Detects an authentication bypass in telnet tracked as CVE-2026-24061. An attacker can supply a specifically crafted USER environment variable (-f root) that is passed to /usr/bin/login. Because this input isn't sanitized an attacker can force the system to skip authentication and login directly as root.

Detection logic

Detection requirements

Platform
IaaSIdentity ProviderLinuxmacOSOffice SuiteWindows

The rule states no platform. This is derived from the ATT&CK technique it maps to.

Log source category
sysmon_for_linux_eventid_1

Known benign triggers

  • It is rare for the telnetd to spawn login process with these arguments.

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