CVE-2026-76925

Flatpak prior to 1.18.1 allows a malicious local user in an active session to use a crafted architecture name to trick the flatpak-system-helper process into creating a root-owned directory tree outside the intended root directory. This requires at least one OCI remote to be configured (common on Fedora). Combined with other vulnerabilities fixed in 1.18.1, it can lead to local root privilege escalation.

In Flatpak before 0.8.7, third-party app repositories could include malicious apps with files having inappropriate permissions, such as setuid or world-writable. These files could be executed by a local attacker or allow writing to world-writable locations.

Flatpak prior to 1.16.4 contains a vulnerability where the Flatpak portal accepts paths in the sandbox-expose options which can be app-controlled symlinks pointing at arbitrary paths. Flatpak run mounts the resolved host path in the sandbox, giving apps access to all host files and can be used as a primitive to gain code execution in the host context.

Flatpak's process ID namespace separation does not prevent a sandboxed app's kill(0, signal) or killpg(0, signal) calls from reaching processes outside the sandbox that share the same process group. A malicious or compromised Flatpak app can use this to cause denial of service by terminating processes outside its sandbox, such as the desktop shell.

A path traversal vulnerability in Flatpak's handling of the files/etc directory during app deployment allows a malicious Flatpak app to cause certain host system files (such as passwd, group, machine-id, or resolv.conf) to be emptied or replaced with a symlink when the app is installed or upgraded. In system-wide installations, the write is performed as root.

Flatpak passes through arbitrary vendor-extension keys unmodified when exporting an application's Desktop Entry (.desktop) and D-Bus Service (.service) files, instead of validating against an allowlist. A malicious Flatpak app can use this to cause denial of service (e.g. forced application restart loops) or to influence host D-Bus/systemd activation behavior beyond what the sandbox is intended to permit.

Flatpak creates temporary child repository directories under the user cache with world-writable permissions (0777). On multi-user systems with a permissive umask, other local users could read or modify the temporary directory used while installing apps or runtimes, potentially causing installation failures (denial of service); tampered content would fail signature/digest verification rather than being trusted.

Flatpak writes the OCI repository authentication token with world-readable permissions (0644) in the system-helper's cache directory, allowing other local users on a multi-user system to read the token and impersonate the authenticated user against the OCI repository. Only OCI-based sources (e.g. as used by Fedora) are affected; libostree-based sources such as Flathub are not.

A path traversal vulnerability in Flatpak's handling of the export/bin directory during app deployment allows a malicious Flatpak app to cause deletion of attacker-chosen files outside the deployment directory when the app is installed or upgraded. In system-wide installations, the deletion is performed as root.

A malicious user can get read-access to files in the flatpak-system-helper context if a system OCI repository is configured, because the OCI code paths in the system helper follow symlinks when importing OCI images that are under the user's control.