CVE-2026-90616: High severity Flatpak Flatpak vulnerability
In Flatpak before 1.18.1, a malicious sandboxed app can obtain arbitrary read and write access to files on the host, which can be escalated to arbitrary code execution on the host, a different vulnerability than CVE-2026-76925. Flatpak creates a few app data directories (e.g., /var/cache, /var/data, /var/config, and /var/tmp) in every sandbox on every app launch where, in some cases, components of the path are attacker-controlled. Missing symlink protection can redirect the directories. Some of these directories are bind-mounted by Flatpak by passing the path (e.g., /home/user/.var/app/APPID/cache/tmp), which contains attacker-controlled directories (tmp) to bwrap --bind SRC DST. bwrap passes the path on to the kernel, which then follows symlinks. A malicious symlink can point to arbitrary locations on the host and it will become mounted inside the sandbox.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
flatpakto a version that resolves this vulnerability.Fixed in 1.18.1 - Compensating control
Mitigate by ensuring the attacker-controlled path component used for Flatpak bind mounts (e.g., /home/user/.var/app/APP_ID/cache/tmp) cannot be a symlink on the host; remove or replace any symlinks in the mount source path so bwrap --bind does not bind through symlink-following to arbitrary locations.
Event History
Frequently Asked Questions
Which installations are affected?
Flatpak versions before 1.18.1 are affected. The vulnerable directories are created in every sandbox on every app launch.
What does an attacker need to exploit this issue?
An attacker needs to run a malicious sandboxed Flatpak app. The supplied vector indicates local access, no privileges, no user interaction, and high attack complexity.
What is the potential impact after exploitation?
A malicious app can gain arbitrary read and write access to host files by redirecting bind-mounted paths with symlinks. This access can be escalated to arbitrary code execution on the host.
How can I determine whether I need to remediate?
Check the installed Flatpak version. Systems running a version earlier than 1.18.1 should be considered affected.