CVE-2025-23395: 
Linux Red Hat vulnerability analysis and mitigation

CVE-2025-23395 is a critical security vulnerability discovered in GNU Screen version 5.0.0 that enables local privilege escalation to root access. The vulnerability affects installations where Screen is configured with setuid-root privileges, primarily impacting Arch Linux and NetBSD systems. The issue was discovered during a comprehensive security audit by the SUSE Security Team and was disclosed in May 2025 (SecurityOnline, OpenWall).

The vulnerability exists in the logfile_reopen() function which fails to drop elevated privileges while operating on user-supplied paths. The issue was introduced via commit 441bca708bd and became part of the 5.0.0 release. When triggered, it allows unprivileged users to create files in arbitrary locations with root ownership, the invoking user's real group ownership, and file mode 0644. The vulnerability can be exploited when Screen believes it needs to reopen the logfile, which occurs when the link count of the originally opened logfile drops to zero or if it unexpectedly changes in size (OpenWall).

The vulnerability allows attackers to achieve local privilege escalation by creating files with root ownership in arbitrary locations. This can be exploited to write new configuration files for tools like sudo, append code to privileged shell scripts, or manipulate other sensitive system files. All data written to the Screen PTY will be logged into the compromised file, potentially leading to system compromise (SecurityOnline).

The issue has been addressed with a patch that reintroduces secure file handling during logfile reopen. SUSE strongly advises against installing Screen with setuid-root privileges. For systems that require multi-user support, it is recommended to implement it as an opt-in feature, possibly restricted to a trusted group. Distributions should explicitly pass the configure switch --with-pty-mode=0620 to ensure safe default permissions (OpenWall).