CVE-2017-9780 in Flatpak
Summary
by MITRE
In Flatpak before 0.8.7, a third-party app repository could include malicious apps that contain files with inappropriate permissions, for example setuid or world-writable. The files are deployed with those permissions, which would let a local attacker run the setuid executable or write to the world-writable location. In the case of the "system helper" component, files deployed as part of the app are owned by root, so in the worst case they could be setuid root.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability described in CVE-2017-9780 represents a critical security flaw in the Flatpak application sandboxing system that affects versions prior to 0.8.7. This issue stems from insufficient validation of file permissions within third-party application repositories, creating a pathway for malicious actors to compromise system security through seemingly legitimate software installations. The vulnerability specifically targets the permission handling mechanisms that Flatpak employs when deploying applications from external repositories, allowing adversaries to inject executables with dangerous file attributes that persist beyond the normal installation process.
The technical flaw manifests when Flatpak processes applications from untrusted repositories and fails to properly sanitize file permissions before deployment. This oversight enables attackers to include files with setuid bits or world-writable permissions within their malicious applications. When these applications are installed and executed, the compromised permissions remain intact, providing attackers with elevated privileges or write access to critical system locations. The vulnerability is particularly concerning because it operates at the installation level rather than during runtime, meaning that the malicious permissions are embedded into the system during the normal application deployment process and can persist until manually corrected.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and persistent backdoor access. When the system helper component is involved, which is responsible for managing privileged operations within the Flatpak environment, the consequences become even more severe. Files deployed with root ownership can be configured with setuid root permissions, granting attackers complete system control through the compromised applications. This creates a scenario where local attackers can leverage the installed malicious applications to gain root privileges, effectively bypassing all normal security boundaries that Flatpak is designed to maintain. The vulnerability undermines the fundamental security model of Flatpak, which relies on strict permission controls and sandboxing to prevent unauthorized system access.
This vulnerability aligns with CWE-276, which addresses improper file permissions, and represents a classic example of inadequate input validation and permission sanitization in software distribution systems. From an ATT&CK framework perspective, this issue maps to privilege escalation techniques through malicious software installation and persistence mechanisms, specifically covering T1068 for local privilege escalation and T1547.001 for persistence through registry run keys or similar mechanisms. The attack vector demonstrates how supply chain compromises can be leveraged to establish persistent access to systems, particularly in environments where users may trust third-party repositories without adequate verification processes.
Mitigation strategies for CVE-2017-9780 require immediate system updates to Flatpak version 0.8.7 or later, which includes enhanced permission validation and sanitization mechanisms. Organizations should implement strict repository verification processes, ensuring that only trusted sources are added to their Flatpak configuration and regularly auditing installed applications for suspicious permission settings. System administrators should conduct comprehensive audits of existing installations to identify and correct any applications that may have been compromised with inappropriate file permissions. Additionally, implementing automated monitoring for setuid and world-writable files can help detect potential exploitation attempts, while maintaining updated security policies that govern third-party software installation and repository management practices.