CVE-2016-10121 in Firejail
Summary
by MITRE
Firejail uses weak permissions for /dev/shm/firejail and possibly other files, which allows local users to gain privileges.
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Analysis
by VulDB Data Team • 08/30/2020
The vulnerability identified as CVE-2016-10121 affects Firejail, a security sandboxing tool designed to provide lightweight application isolation by leveraging Linux namespaces and seccomp-bpf. This particular flaw stems from the improper permission settings applied to critical temporary files within the /dev/shm filesystem, specifically the /dev/shm/firejail file path. The issue represents a privilege escalation vulnerability that allows local attackers to manipulate these poorly protected resources and potentially elevate their privileges within the system. Firejail operates by creating isolated environments for applications, and the weakness in file permissions undermines this security model by creating an attack vector that bypasses the intended isolation mechanisms.
The technical flaw manifests through the use of weak file permissions that do not adequately restrict access to the firejail temporary file in shared memory. This file, along with potentially other temporary files created by Firejail, is typically created with overly permissive settings that allow any local user to modify or replace the file contents. The vulnerability is classified under CWE-732 as improper permission assignment for critical resources, where the system fails to properly restrict access to security-critical temporary files. When a local user can manipulate these files, they can potentially inject malicious content that gets executed with elevated privileges, as Firejail may read and process these files during its operation. This weakness directly violates the principle of least privilege and creates a direct path for privilege escalation attacks.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it fundamentally compromises the security model that Firejail is designed to provide. Attackers can exploit this weakness by creating symbolic links or replacing the vulnerable files with malicious content that gets executed in the context of the Firejail process. This creates a scenario where local users can gain elevated privileges without requiring authentication or exploiting other system vulnerabilities. The attack vector is particularly concerning because it leverages the legitimate functionality of Firejail itself, making the exploitation more difficult to detect and trace. The vulnerability affects systems where Firejail is installed and used, potentially impacting a wide range of applications that rely on sandboxed execution environments. This weakness can be particularly dangerous in multi-user environments where users have varying levels of access but should not be able to escalate their privileges through the sandboxing mechanism.
Mitigation strategies for CVE-2016-10121 should focus on implementing proper file permission controls for temporary files created by Firejail. System administrators should ensure that temporary files in /dev/shm are created with restrictive permissions that only allow the intended process to access them. The fix typically involves modifying Firejail's source code to properly set file permissions during temporary file creation, ensuring that these files are not world-writable or group-writable. Additionally, regular security audits should verify that temporary files created by sandboxing tools maintain appropriate access controls. Organizations should also consider implementing monitoring solutions that can detect unauthorized modifications to critical temporary files, as outlined in the attack patterns described by the MITRE ATT&CK framework under privilege escalation techniques. Updates to Firejail versions that address this specific weakness are crucial, as this vulnerability directly impacts the core security guarantees provided by the sandboxing tool. The remediation process should include verifying that all temporary files created by Firejail are properly secured and that the sandboxing environment maintains its isolation properties.