CVE-2016-10318 in Linux
Summary
by MITRE
A missing authorization check in the fscrypt_process_policy function in fs/crypto/policy.c in the ext4 and f2fs filesystem encryption support in the Linux kernel before 4.7.4 allows a user to assign an encryption policy to a directory owned by a different user, potentially creating a denial of service.
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Analysis
by VulDB Data Team • 11/27/2022
The vulnerability identified as CVE-2016-10318 represents a critical authorization flaw in the Linux kernel's filesystem encryption implementation that affects both ext4 and f2fs filesystems. This issue stems from a missing authorization check within the fscrypt_process_policy function located in fs/crypto/policy.c, which governs how encryption policies are applied to filesystem directories. The flaw allows unprivileged users to manipulate encryption policies on directories they do not own, creating a significant security boundary violation that undermines the fundamental principle of user isolation and access control within the Linux operating system.
The technical nature of this vulnerability can be categorized under CWE-693, which deals with Protection Mechanism Failure, specifically involving inadequate authorization checks. The flaw occurs when the fscrypt_process_policy function fails to properly validate whether the user attempting to assign an encryption policy has sufficient privileges to modify the target directory. This missing validation enables a malicious user to assign encryption policies to directories owned by other users, potentially leading to unintended consequences including the ability to render files inaccessible to their legitimate owners. The vulnerability exists in kernel versions prior to 4.7.4, making it a widespread issue affecting numerous Linux distributions and systems that have not been properly updated.
From an operational perspective, this vulnerability creates multiple attack vectors that can be leveraged for both privilege escalation and denial of service scenarios. An attacker with local access can exploit this flaw to manipulate encryption policies on directories belonging to other users, potentially causing files to become inaccessible or corrupted. The impact extends beyond simple access control violations as it can be used to create a denial of service condition where legitimate users lose access to their own files due to unauthorized encryption policy changes. This vulnerability aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', and can also be classified under T1499 for 'Endpoint Denial of Service' when used to render systems unusable through file access manipulation.
The security implications of this vulnerability are particularly concerning given that filesystem encryption is a core feature designed to protect user data confidentiality and integrity. When users can bypass authorization checks to modify encryption policies, they effectively gain the ability to manipulate the security controls that protect other users' data. This creates a scenario where a low-privileged user can potentially disrupt the normal operation of a system by altering encryption settings on files owned by other users. The vulnerability demonstrates a fundamental failure in the kernel's access control mechanisms and highlights the importance of proper authorization validation in security-critical subsystems.
Mitigation strategies for CVE-2016-10318 primarily focus on immediate kernel updates to versions 4.7.4 or later where the authorization check has been properly implemented. System administrators should prioritize patching affected systems to prevent exploitation, particularly in environments where multiple users share the same system and where filesystem encryption is enabled. Additionally, monitoring for unusual filesystem encryption policy changes can serve as an early detection mechanism, though this requires careful implementation to avoid false positives while maintaining security effectiveness. Organizations should also review their filesystem encryption configurations and access controls to ensure that proper user isolation is maintained, implementing additional security measures such as mandatory access controls or enhanced logging to detect unauthorized policy modifications. The vulnerability serves as a reminder of the critical importance of proper authorization checking in kernel space and the potential consequences when such checks are omitted or improperly implemented in security-sensitive components.