CVE-2017-7374 in Linux
Summary
by MITRE
Use-after-free vulnerability in fs/crypto/ in the Linux kernel before 4.10.7 allows local users to cause a denial of service (NULL pointer dereference) or possibly gain privileges by revoking keyring keys being used for ext4, f2fs, or ubifs encryption, causing cryptographic transform objects to be freed prematurely.
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Analysis
by VulDB Data Team • 11/24/2022
The vulnerability described in CVE-2017-7374 represents a critical use-after-free condition within the Linux kernel's cryptographic subsystem, specifically in the file system crypto module located at fs/crypto/. This flaw exists in kernel versions prior to 4.10.7 and demonstrates how improper memory management can lead to severe system instability and potential privilege escalation. The vulnerability arises from the improper handling of cryptographic transform objects when keyring keys are revoked during active encryption operations, creating a scenario where memory that has been freed is subsequently accessed, leading to either system crashes or unauthorized privilege elevation.
The technical implementation of this vulnerability stems from the kernel's handling of encryption keys for ext4, f2fs, and ubifs file systems where cryptographic transform objects are prematurely freed when keyring keys are revoked. When a key is revoked while being actively used for file system encryption, the kernel's reference counting mechanism fails to properly manage the lifecycle of the cryptographic transform objects. This creates a race condition where the memory containing these objects is freed but the system continues to reference them, resulting in a NULL pointer dereference that causes system crashes or potentially allows attackers to execute arbitrary code with elevated privileges. The vulnerability specifically targets the cryptographic subsystem's interaction with file system encryption mechanisms, making it particularly dangerous in environments where encrypted file systems are actively used.
The operational impact of CVE-2017-7374 extends beyond simple denial of service scenarios to encompass potential privilege escalation and system compromise. Local attackers who can manipulate keyring operations and trigger the revocation of encryption keys can exploit this vulnerability to either crash the system through NULL pointer dereferences or potentially gain root privileges by leveraging the use-after-free condition to execute code in kernel space. This vulnerability is particularly concerning in multi-user environments where local users might attempt to exploit it for privilege escalation, and in systems where encrypted file systems are prevalent such as mobile devices, servers handling sensitive data, or embedded systems where file system encryption is commonly employed. The attack vector requires local access and the ability to manipulate keyring operations, making it difficult to exploit remotely but potentially devastating when successfully executed.
Mitigation strategies for CVE-2017-7374 primarily focus on kernel version updates and system hardening measures. The most effective immediate solution is upgrading to Linux kernel version 4.10.7 or later where the vulnerability has been patched through proper memory management fixes in the cryptographic subsystem. System administrators should also implement strict access controls to limit local user privileges and monitor keyring operations that could potentially trigger this vulnerability. The patch addresses the underlying use-after-free condition by ensuring proper reference counting and memory management when cryptographic transform objects are freed during key revocation operations. Organizations should also consider implementing kernel lockdown mechanisms and other security controls to limit the potential impact of such vulnerabilities in their environments, aligning with defense-in-depth principles recommended in cybersecurity frameworks.
This vulnerability maps directly to CWE-416 which describes the use of freed memory condition, and it aligns with several ATT&CK techniques including privilege escalation through kernel exploits and defense evasion by causing system instability. The vulnerability demonstrates how seemingly routine operations like key revocation can lead to critical security flaws when proper memory management protocols are not followed, highlighting the importance of rigorous code review and security testing in kernel development. The exploitation of this vulnerability requires understanding of both kernel internals and file system encryption mechanisms, making it a sophisticated attack that targets the fundamental security architecture of the Linux operating system and the cryptographic subsystem that protects data at rest.