CVE-2016-10117 in Firejail
Summary
by MITRE
Firejail does not restrict access to --tmpfs, which allows local users to gain privileges, as demonstrated by mounting over /etc.
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Analysis
by VulDB Data Team • 08/30/2020
CVE-2016-10117 represents a critical privilege escalation vulnerability within the Firejail sandboxing framework that operates under the common weakness enumeration CWE-276. This flaw exists in the handling of temporary filesystem mounts and specifically affects the --tmpfs option functionality that Firejail provides to isolate applications within secure containers. The vulnerability stems from insufficient access controls that permit local users to manipulate temporary filesystem mounts in ways that bypass the intended security boundaries of the sandboxing mechanism.
The technical implementation of this vulnerability allows an attacker to exploit the improper restriction of filesystem access by mounting temporary filesystems over critical system directories such as /etc, which contains essential configuration files and system settings. When Firejail processes the --tmpfs command line option, it fails to properly validate or restrict the mount points that can be specified, enabling local users to create temporary filesystems that overlay sensitive system paths. This creates a scenario where malicious code running within a Firejail sandbox can gain elevated privileges by modifying system configuration files or replacing critical binaries in the overlaid directories.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and data integrity breaches. Attackers can leverage this flaw to modify system-wide configurations, inject malicious code into critical system components, or establish persistent access mechanisms. The vulnerability particularly affects systems where Firejail is used to run untrusted applications with reduced privileges, as the sandbox environment becomes compromised and loses its protective value. This weakness directly violates the fundamental security principle of least privilege and undermines the trust model that sandboxing frameworks are designed to maintain.
Mitigation strategies for CVE-2016-10117 should focus on immediate patching of Firejail versions containing this vulnerability while implementing additional operational controls. System administrators should review all Firejail configurations to ensure that --tmpfs options are properly restricted and validated before execution. The mitigation approach aligns with ATT&CK technique T1068 which addresses privilege escalation through local exploitation and emphasizes the importance of validating and restricting system call parameters. Organizations should also consider implementing monitoring solutions to detect unauthorized filesystem mount operations and establish baseline configurations that prevent the exploitation of such vulnerabilities. The fix typically involves modifying Firejail's mount validation logic to ensure that temporary filesystems cannot be mounted over critical system directories, thereby maintaining the integrity of the sandboxed environment and preserving the security boundaries that the tool is designed to enforce.