CVE-2021-21381 Explained : Impact and Mitigation

CVE-2021-21381 is a vulnerability in Flatpak, a system for building and running sandboxed desktop applications on Linux. The vulnerability allows attackers to gain access to files not authorized by the app's permissions by exploiting special tokens in the .desktop file of a Flatpak app.

Understanding CVE-2021-21381

Flatpak versions 0.9.4 through 1.10.2 are affected by the vulnerability, which involves the 'file forwarding' feature. A malicious app publisher can manipulate the Exec field in a .desktop file to trick Flatpak into granting access to sensitive files.

What is CVE-2021-21381?

The CVE-2021-21381 vulnerability in Flatpak allows unauthorized access to files by using special tokens in the .desktop file. Attackers can exploit this to access files beyond the app's usual permissions.

The Impact of CVE-2021-21381

A successful exploitation of CVE-2021-21381 could lead to unauthorized access to sensitive files and data on the affected system. It poses a high integrity impact threat by allowing an attacker to access files not meant to be available.

Technical Details of CVE-2021-21381

The vulnerability arises from improper handling of special tokens in the .desktop file of Flatpak apps. By inserting

@@

or

@@u

in the Exec field, an attacker can manipulate Flatpak into exposing restricted files to the app.

Vulnerability Description

The flaw in Flatpak versions before 1.10.2 allows malicious actors to exploit the 'file forwarding' feature using special tokens in the .desktop file to access unauthorized files.

Affected Systems and Versions

Flatpak versions from 0.9.4 to 1.10.1 are affected by CVE-2021-21381. Systems using these vulnerable versions are at risk of unauthorized file access.

Exploitation Mechanism

Attackers can leverage the CVE-2021-21381 vulnerability by crafting a specially designed .desktop file with

@@

or

@@u

tokens in the Exec field. This manipulates Flatpak into granting access to protected files.

Mitigation and Prevention

Users and administrators can take immediate steps to mitigate the risks posed by CVE-2021-21381 and prevent unauthorized access to sensitive files.

Immediate Steps to Take

Install Flatpak version 1.10.2 or later to address the vulnerability. Avoid downloading or installing Flatpak apps from untrusted sources to reduce the risk of exploitation.

Long-Term Security Practices

Regularly update Flatpak to the latest version and monitor official security advisories for any potential vulnerabilities that may arise. Ensure that the .desktop files of Flatpak apps do not contain suspicious special tokens.

Patching and Updates

Apply the necessary patches and updates provided by the Flatpak project to secure the system against CVE-2021-21381.