Overview

The Common Vulnerabilities and Exposures (CVE) system has recently identified a critical security vulnerability, CVE-2025-23395, affecting Screen 5.0.0. This software, when run with setuid-root privileges, fails to drop these elevated privileges while operating on a user-supplied path. This vulnerability holds grave implications for all systems running the affected version of Screen as it allows unprivileged users to exploit this flaw and potentially gain root access, thereby compromising the entire system. Given the widespread use of Screen, this vulnerability holds potential for extensive damage and is of significant concern to system administrators and cybersecurity professionals alike.

Vulnerability Summary

CVE ID: CVE-2025-23395
Severity: High (7.8)
Attack Vector: Local
Privileges Required: Low
User Interaction: Required
Impact: System compromise, data leakage

Affected Products

Product | Affected Versions

Screen | 5.0.0

How the Exploit Works

This vulnerability arises from the program’s mishandling of user-supplied paths. When Screen 5.0.0 runs with setuid-root privileges, it does not correctly drop these privileges when operating on a user-supplied path. This loophole allows an unprivileged user to create files in arbitrary locations with root ownership. The files also retain the invoking user’s group ownership and file mode 0644. In essence, all data written to the Screen PTY will be logged into this file. This situation can be exploited to escalate to root privileges, granting the attacker complete control over the compromised system.

Conceptual Example Code

Here’s a
conceptual
example of how the vulnerability might be exploited using a shell command:

# command to start Screen with setuid-root privileges
/usr/bin/screen -D -m -L /root/privileged.file
# command to write data to the Screen PTY
echo "malicious_command" > /dev/pts/X # X corresponds to the screen session PTY
# The above command logs the data into /root/privileged.file with root ownership
# The attacker can thus manipulate this file to gain root access

This example serves to illustrate the potential exploitation of the vulnerability. Actual exploitation may vary based on the system’s configuration and the attacker’s capabilities.