CVE-2014-9644 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 parenthesized module template expression in the salg_name field, as demonstrated by the vfat(aes) expression, a different vulnerability than CVE-2013-7421.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability described in CVE-2014-9644 represents a critical security flaw in the Linux kernel's Crypto API implementation that affects versions prior to 3.18.5. This issue resides within the AF_ALG socket family which provides userspace access to kernel cryptographic algorithms and operations. The vulnerability specifically manifests when a local user executes a bind system call against an AF_ALG socket with a specially crafted salg_name field containing a parenthesized module template expression. This particular flaw enables arbitrary kernel module loading through seemingly benign cryptographic operations, creating a significant attack surface that bypasses normal kernel module loading restrictions.
The technical exploitation of this vulnerability relies on the improper validation of input parameters within the AF_ALG socket implementation. When a user provides a salg_name field containing expressions like vfat(aes), the kernel's cryptographic subsystem incorrectly interprets these as module loading directives rather than as standard algorithm specifications. This misinterpretation occurs because the Crypto API fails to properly sanitize or validate the module template expressions, allowing malicious input to trigger kernel module loading mechanisms. The vulnerability specifically affects the kernel's module loading infrastructure where it processes these parenthesized expressions without adequate security checks, potentially leading to privilege escalation or system compromise.
From an operational perspective, this vulnerability represents a local privilege escalation vector that allows attackers with limited user access to load arbitrary kernel modules, potentially gaining root privileges or executing arbitrary code with kernel-level permissions. The impact extends beyond simple privilege escalation as it enables attackers to load malicious kernel modules that can persist across reboots, modify system behavior, or establish backdoors. The vulnerability's classification as a local privilege escalation issue aligns with CWE-264, which addresses permissions, privileges, and access controls in kernel-level operations. Additionally, this vulnerability demonstrates characteristics consistent with ATT&CK technique T1068, which involves exploiting local privilege escalation opportunities through kernel vulnerabilities.
The exploitation chain begins with a local user creating an AF_ALG socket and then binding it with a malicious salg_name field containing parenthesized module expressions. The kernel's insufficient input validation causes it to interpret these expressions as legitimate module loading commands, leading to the loading of unauthorized kernel modules. This mechanism differs from CVE-2013-7421, which affected different kernel subsystems, making CVE-2014-9644 a distinct but related vulnerability within the kernel's cryptographic framework. The vulnerability's persistence and impact make it particularly dangerous as loaded kernel modules can operate with full system privileges and access to all kernel memory spaces.
Mitigation strategies for this vulnerability require immediate kernel version updates to 3.18.5 or later, where the Crypto API implementation includes proper input validation and sanitization for AF_ALG socket operations. Organizations should also implement monitoring for suspicious kernel module loading activities and restrict local user access to cryptographic operations where possible. System administrators should consider implementing kernel hardening measures such as module signing requirements and kernel lockdown mechanisms. The fix addresses the root cause by ensuring that parenthesized expressions in the salg_name field are properly validated and sanitized before any kernel module loading operations are initiated, preventing the exploitation of this specific input validation weakness.