CVE-2021-21261 Explained : Impact and Mitigation

A bug was discovered in the

flatpak-portal

service that can allow sandboxed applications to execute arbitrary code on the host system, posing a sandbox escape threat.

Understanding CVE-2021-21261

This CVE pertains to a vulnerability in Flatpak, affecting versions >= 0.11.4 and < 1.8.5, as well as >= 1.9.0 and < 1.10.0.

What is CVE-2021-21261?

Flatpak is a system designed for building, distributing, and running sandboxed desktop applications on Linux. The bug in the

flatpak-portal

service allows sandboxed apps to run arbitrary code on the host system.

The Impact of CVE-2021-21261

This vulnerability has a base severity of HIGH, with a CVSS base score of 7.3. It can lead to a compromise of system confidentiality with low integrity impact.

Technical Details of CVE-2021-21261

The vulnerability arises from the passing of caller-specified environment variables to non-sandboxed processes on the host system by the Flatpak portal service.

Vulnerability Description

The

flatpak-portal

service passes environment variables to non-sandboxed processes, enabling a malicious app to execute arbitrary code on the host system outside the sandbox environment.

Affected Systems and Versions

Flatpak versions >= 0.11.4 and < 1.8.5, as well as >= 1.9.0 and < 1.10.0, are impacted by this vulnerability.

Exploitation Mechanism

A compromised Flatpak app could set environment variables that are trusted by the

flatpak run

command, enabling the execution of arbitrary code outside the sandbox.

Mitigation and Prevention

To mitigate this vulnerability, users are advised to update Flatpak to versions 1.8.5 or 1.10.0.

Immediate Steps to Take

Prevent the

flatpak-portal

service from starting as a short-term measure to mitigate the vulnerability.

Long-Term Security Practices

Regularly update Flatpak and other software components to ensure protection against potential security threats.

Patching and Updates

Apply the fixed versions 1.8.5 and 1.10.0 of Flatpak to eliminate the sandbox escape vulnerability.