KDE Konsole Terminal Emulator Vulnerability Allows Remote Code Execution Through Malicious URLs

A critical security vulnerability in KDE’s popular Konsole terminal emulator has been discovered that could allow attackers to execute arbitrary code on users’ systems through malicious website URLs.

The vulnerability, assigned CVE-2025-49091, affects Konsole versions prior to 25.04.2 and poses a significant risk to Linux desktop users, particularly those running KDE Plasma environments.

The vulnerability specifically targets systems where KTelnetService and a vulnerable version of Konsole are installed, but where at least one of the standard networking programs—telnet, rlogin, or ssh—is missing.

This configuration was notably present in the default installation of Fedora KDE Plasma Desktop 42, where both telnet and rlogin were absent while Konsole version 24.12.3 was installed.

The attack vector exploits KDE’s URL scheme handlers for telnet://, rlogin://, and ssh:// protocols. When users visit a malicious website and allow these URL schemes to be opened in their browser, the vulnerability can be triggered.

The exploitation requires user interaction, specifically accepting a browser prompt to “Allow this site to open the telnet link with KTelnetService,” but this represents a relatively low barrier for social engineering attacks.

The discovery of this vulnerability was inspired by a similar issue found in April 2025 involving Yelp’s ghelp:// scheme handler, prompting security researchers to investigate other potentially vulnerable scheme handlers installed on Linux desktop systems.

Konsole Terminal Emulator Vulnerability

The attack follows a sophisticated multi-step process that combines web-based file downloads with URL scheme manipulation.

First, a malicious website automatically downloads a script file to the user’s Downloads directory using a base64-encoded data URL.

The script contains arbitrary commands that the attacker wishes to execute on the target system.

Following the download, the website redirects the user to a specially crafted telnet URL that references the downloaded script file using the path telnet:///proc/self/cwd/Downloads/evil.

When KTelnetService processes this URL, it attempts to launch Konsole with the command /usr/bin/konsole --noclose -e telnet /proc/self/cwd/Downloads/evil.

However, since the telnet program is not installed on the vulnerable system, Konsole’s fallback mechanism activates.

Instead of failing gracefully, Konsole executes /bin/bash while maintaining the original argument /proc/self/cwd/Downloads/evil, effectively running the malicious script.

Users would see a warning message stating “Could not find ‘telnet’, starting ‘/bin/bash’ instead,” followed by the execution of the downloaded script.

Disclosure Timeline

KDE addressed this vulnerability in Konsole version 25.04.2 through commit 09d20dea, which implements proper argument clearing when the requested command is not found.

This fix ensures that if telnet, rlogin, or ssh programs are missing, Konsole will execute only /bin/bash without any potentially dangerous arguments.

The vulnerability disclosure followed responsible security practices. The issue was initially reported to KDE’s security team on April 16, 2025, and was promptly acknowledged the same day.

After confirming the exploit and developing fixes, KDE published their security advisory on June 9, 2025, followed by this detailed technical write-up on June 10, 2025. Users are strongly advised to update to Konsole 25.04.2 or later to mitigate this security risk.

Find this Story Interesting! Follow us on LinkedIn and X to Get More Instant Updates.