CVE-2016-7097 in Linux
Summary
by MITRE
The filesystem implementation in the Linux kernel through 4.8.2 preserves the setgid bit during a setxattr call, which allows local users to gain group privileges by leveraging the existence of a setgid program with restrictions on execute permissions.
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Analysis
by VulDB Data Team • 09/26/2022
The vulnerability identified as CVE-2016-7097 represents a significant security flaw in the Linux kernel's filesystem implementation that affects versions through 4.8.2. This issue exploits a fundamental mismanagement of file permissions during extended attribute operations, creating an avenue for privilege escalation that directly impacts system security. The flaw specifically manifests when the setxattr system call preserves the setgid bit on files, which should normally be stripped during certain operations to maintain proper security boundaries. The vulnerability exists because the kernel fails to properly enforce the expected behavior of setgid programs, particularly when these programs have execute permissions restricted. This creates a scenario where local users can manipulate file attributes to gain unintended group privileges, effectively bypassing the security model that should prevent such escalation. The technical root cause stems from the kernel's failure to properly validate and enforce permission semantics during extended attribute modifications, allowing malicious users to exploit the interaction between setgid bits and extended attributes.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially compromise entire system security domains. Attackers can leverage this flaw to elevate their privileges from a regular user to a group member with elevated permissions, particularly when targeting setgid programs that are designed to run with specific group privileges. This type of vulnerability falls under the CWE-276 category of improper privilege management, where the system fails to properly enforce access controls during attribute modifications. The vulnerability demonstrates a clear path for local privilege escalation that can be exploited by malicious users who understand the interaction between setgid programs and extended attributes. The security implications are particularly severe because setgid programs are designed to run with elevated privileges, and the preservation of the setgid bit during setxattr operations undermines the fundamental security model of Unix-like systems. This allows attackers to effectively circumvent the intended security boundaries and gain access to resources that should be restricted to specific group memberships.
Mitigation strategies for CVE-2016-7097 require both immediate system updates and careful administrative oversight of setgid programs. The primary remediation involves upgrading to a Linux kernel version that addresses this specific vulnerability, as the flaw exists in the core filesystem implementation and cannot be effectively patched through configuration changes alone. System administrators should also implement comprehensive monitoring of extended attribute operations, particularly those involving setgid files, to detect potential exploitation attempts. The vulnerability's exploitation requires specific conditions including the presence of setgid programs with restricted execute permissions, making it crucial for administrators to audit their system's setgid programs and ensure proper permission management. Organizations should consider implementing additional security controls such as mandatory access controls or enhanced privilege separation mechanisms to limit the potential impact of such vulnerabilities. The ATT&CK framework categorizes this as a privilege escalation technique, specifically targeting the 'Setuid and Setgid' tactic where attackers manipulate program execution contexts to gain elevated privileges. Security teams should also establish procedures for regularly reviewing and updating system configurations to prevent the creation of vulnerable setgid programs and maintain proper file permission semantics throughout the system.