CVE-2026-53759: linuxfabrik-lib Path Traversal Flaw

CVE-2026-53759 Overview

CVE-2026-53759 affects linuxfabrik-lib, a Python library that provides modules for database access, caching, shell execution, and API integrations. Versions prior to 4.2.0 create SQLite databases at predictable paths inside the shared /tmp directory and follow attacker-created symbolic links at those locations. A local attacker who controls a monitoring account can plant a symlink such as /tmp/linuxfabrik-monitoring-plugins-docker-stats.db and then trigger a sudo-authorized plugin. The root-privileged process then creates or modifies the symlink target. The issue is fixed in version 4.2.0 and is tracked as an insecure temporary file weakness [CWE-377].

Critical Impact
A local attacker can overwrite arbitrary files as root, cause denial of service, or tamper with existing SQLite databases through crafted rollback journals or write-ahead logs.

Affected Products

linuxfabrik-lib versions prior to 4.2.0
Linuxfabrik Monitoring Plugins integrations that consume lib.db_sqlite
Systems where sudo-authorized Linuxfabrik plugins run with elevated privileges

Discovery Timeline

2026-08-18 - CVE-2026-53759 published to NVD
2026-08-18 - Last updated in NVD database

Technical Details for CVE-2026-53759

Vulnerability Analysis

The flaw resides in db_sqlite.py, which constructs SQLite database file paths inside the world-writable /tmp directory using predictable, static filenames. When a Linuxfabrik plugin runs, the library opens or creates these SQLite files without verifying whether the target path is a symbolic link. If an attacker has pre-created a symlink at the expected path, the library follows it, and any file operation performed by the elevated process is redirected to the attacker-chosen target.

Because many Linuxfabrik monitoring plugins are wrapped by sudo rules, the SQLite operations run as root. This creates a local privilege escalation primitive. The attacker gains three concrete capabilities: arbitrary file creation or overwrite as root, denial of service by redirecting writes to critical files, and controlled corruption of legitimate SQLite databases through crafted rollback journals or write-ahead log files.

Root Cause

The root cause is insecure use of a shared temporary directory for persistent state, combined with the absence of O_NOFOLLOW semantics or a symlink safety check before opening the database file. The path was globally predictable, and /tmp permissions allow any local user to create files and symlinks at chosen names. This pattern maps to [CWE-377] Insecure Temporary File.

Attack Vector

Exploitation requires local access with an account that can create files in /tmp and the ability to trigger execution of a sudo-authorized Linuxfabrik plugin, typically a monitoring user. The attacker creates a symbolic link at the predictable database path pointing at a target file such as /etc/cron.d/attacker or an existing SQLite database used by another service. When the plugin runs, the root process opens the symlink and performs writes against the target path.

No verified exploit code has been published. Technical details are available in the GitHub Security Advisory GHSA-r35r-fpx2-jgr4 and the fix commit.

Detection Methods for CVE-2026-53759

Indicators of Compromise

Unexpected symbolic links in /tmp with names matching the pattern linuxfabrik-monitoring-plugins-*.db, *.db-journal, or *.db-wal
Files owned by root appearing at unusual paths after Linuxfabrik plugin execution
SQLite journal or write-ahead log artifacts referencing paths outside the expected cache directory

Detection Strategies

Audit /tmp for pre-existing files or symlinks matching Linuxfabrik SQLite database naming conventions before plugin execution
Enable Linux audit rules on openat and link syscalls originating from Linuxfabrik plugin processes to detect symlink following
Compare installed linuxfabrik-lib package version against the fixed release 4.2.0 across the fleet

Monitoring Recommendations

Log all sudo invocations of Linuxfabrik monitoring plugins and correlate with file creation events under /tmp
Alert on any file write by a root-privileged Python process to paths outside expected plugin cache directories
Monitor monitoring service accounts for anomalous filesystem activity in shared temporary directories

How to Mitigate CVE-2026-53759

Immediate Actions Required

Upgrade linuxfabrik-lib to version 4.2.0 or later on all systems running Linuxfabrik monitoring plugins
Review sudoers configurations that grant plugin execution privileges to non-root monitoring accounts and restrict scope where possible
Remove any residual SQLite artifacts from /tmp created by prior versions and verify no attacker-planted symlinks remain

Patch Information

The vulnerability is fixed in linuxfabrik-lib v4.2.0. The Monitoring Plugins integration was updated so plugin caches now route through lib.db_sqlite.get_db_path(), which returns a secured per-user directory instead of a shared /tmp path. Details are documented in the v4.2.0 changelog and the v4.2.0 release notes.

Workarounds

If immediate upgrade is not possible, restrict shell access for monitoring accounts to prevent symlink planting in /tmp
Configure Linuxfabrik plugins to use a private, non-world-writable cache directory via environment configuration where supported
Apply PrivateTmp=yes in systemd unit files for services that invoke Linuxfabrik plugins to isolate their /tmp view

bash

# Example systemd hardening for services invoking Linuxfabrik plugins
[Service]
PrivateTmp=yes
ProtectSystem=strict
ReadWritePaths=/var/lib/linuxfabrik
NoNewPrivileges=yes