CVE-2026-96282

A malicious Flatpak extension can probe the host filesystem to determine what files and directories exist at arbitrary paths, and host directory listings can be disclosed to sandboxed applications using the extension. Additionally, unvalidated extension metadata can cause extension content to be mounted at unintended locations inside the sandbox.

Red Hat estimates the CVSSv3.1 vector of CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N.

Exploitation requires a user to install a malicious Flatpak extension and use it with an application (AV:N, PR:N). The victim must specifically use a malicious extension in combination with a consuming application, and then launch that application (AC:H, UI:R). When Flatpak launches an application, it performs host-side file operations inside extension content directories using path-based APIs that follow symlinks without confinement; a malicious extension can place symlinks pointing at arbitrary host paths, which are followed both when checking for the .ref lock marker file and when iterating merge_dirs directories. For merge_dirs, the host-side directory listing is reflected into the sandbox as symlinks the application can enumerate. Separately, extension metadata fields (directory, subdir_suffix, add_ld_path, merge_dirs) are not validated for path traversal, so absolute paths or .. components can cause extension content to be mounted at unintended sandbox locations, potentially overriding runtime directories.

These operations run at the invoking user's own privilege level rather than via the privileged system-helper (S:U). While the flaw allows probing for file/directory existence and disclosing filenames via reflected directory listings, no file contents are disclosed (C:N). Invalidated extension metadata can redirect mounts within the launched application's own sandbox, potentially overriding runtime directories used by that app (I:L). There is no availability impact (A:N).

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Avoid installing Flatpak extensions from non-trusted sources.