CVE-2026-96282
Description
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.
Statement
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).
Mitigation
Avoid installing Flatpak extensions from non-trusted sources.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 3.1 | N/A | 3.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | Required | N/A | Required |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N
Understanding the Weakness (CWE)
Confidentiality,Integrity,Access Control
Technical Impact: Read Files or Directories; Modify Files or Directories; Bypass Protection Mechanism
An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism then an attacker may be able to bypass the mechanism.
Other
Technical Impact: Execute Unauthorized Code or Commands
Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.
Acknowledgements
Upstream acknowledges Sebastian Wick as the original reporter.
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