CVE-2013-7421 in Linux
Summary
by MITRE
The Crypto API in the Linux kernel before 3.18.5 allows local users to load arbitrary kernel modules via a bind system call for an AF_ALG socket with a module name in the salg_name field, a different vulnerability than CVE-2014-9644.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability described in CVE-2013-7421 represents a significant security flaw within the Linux kernel's Crypto API implementation that affects versions prior to 3.18.5. This issue specifically targets the AF_ALG socket family which provides userspace access to kernel crypto algorithms and operates under the principle of providing a unified interface for cryptographic operations. The vulnerability arises from insufficient input validation within the bind system call mechanism for AF_ALG sockets, where the salg_name field can be manipulated to specify arbitrary kernel module names. This represents a privilege escalation vector that allows local attackers to load potentially malicious kernel modules without proper authorization, bypassing normal kernel module loading restrictions that typically require root privileges or specific kernel capabilities.
The technical exploitation of this vulnerability occurs through the manipulation of the AF_ALG socket interface during the bind operation. When a user process attempts to bind to an AF_ALG socket, the kernel validates the socket address structure and processes the salg_name field which contains the name of the cryptographic algorithm or module to be loaded. In vulnerable versions, this field is not properly sanitized or validated, allowing an attacker to specify any kernel module name that they wish to load. The kernel's module loading mechanism then attempts to load this specified module without adequate verification of the requester's privileges or the module's legitimacy, creating a pathway for arbitrary code execution at kernel level. This flaw operates under the principle of privilege escalation through improper access control mechanisms and represents a classic case of insufficient input validation leading to unauthorized system modification.
The operational impact of CVE-2013-7421 extends beyond simple privilege escalation to encompass potential full system compromise and persistent backdoor capabilities. Local attackers who can execute code on a target system can leverage this vulnerability to load malicious kernel modules that can intercept cryptographic operations, modify kernel memory, or establish persistent access mechanisms. The vulnerability's classification aligns with CWE-20: Improper Input Validation, as the system fails to properly validate the module name provided in the salg_name field. This allows for the loading of unauthorized kernel modules which can then be used to manipulate kernel behavior, potentially enabling information disclosure, privilege escalation to root access, or the establishment of covert communication channels. The attack vector is particularly concerning because it requires only local user access, making it exploitable in scenarios where attackers have already gained user-level access but need to elevate privileges to achieve full system control.
Mitigation strategies for this vulnerability require immediate kernel version updates to 3.18.5 or later, as this represents the most effective and comprehensive solution to address the underlying validation flaw. Organizations should prioritize patching systems running vulnerable kernel versions, particularly those in production environments where local access might be compromised. Additionally, system administrators should implement monitoring for unauthorized kernel module loading activities and review system logs for suspicious module insertion patterns. The vulnerability's remediation aligns with ATT&CK technique T1547.006: Kernel Modules and Extensions, which focuses on the use of kernel modules for persistence and privilege escalation. Network segmentation and access control measures should be strengthened to limit local user access where possible, while also implementing kernel module signing policies to ensure only trusted modules can be loaded. System hardening practices including disabling unnecessary kernel features and implementing secure boot mechanisms can further reduce the attack surface and prevent exploitation of this and similar vulnerabilities.