CVE-2014-4656 in Linux
Summary
by MITRE
Multiple integer overflows in sound/core/control.c in the ALSA control implementation in the Linux kernel before 3.15.2 allow local users to cause a denial of service by leveraging /dev/snd/controlCX access, related to (1) index values in the snd_ctl_add function and (2) numid values in the snd_ctl_remove_numid_conflict function.
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Analysis
by VulDB Data Team • 01/18/2022
The vulnerability described in CVE-2014-4656 represents a critical security flaw within the Advanced Linux Sound Architecture (ALSA) subsystem of the Linux kernel. This issue affects versions prior to 3.15.2 and specifically targets the sound/core/control.c file where the ALSA control implementation resides. The vulnerability manifests through two distinct integer overflow conditions that can be exploited by local attackers with access to /dev/snd/controlCX devices, which are typically accessible to users in the audio group or those with appropriate privileges. These integer overflows occur during the processing of control elements within the ALSA framework, creating a potential vector for denial of service attacks that can disrupt audio functionality on affected systems.
The technical exploitation of this vulnerability involves two primary attack vectors that leverage integer overflow conditions in different functions within the ALSA control subsystem. The first overflow occurs in the snd_ctl_add function where index values are processed, while the second overflow happens in the snd_ctl_remove_numid_conflict function involving numid values. Both conditions result from inadequate input validation and bounds checking within the kernel's sound subsystem implementation. When these integer overflows occur, they can lead to unpredictable behavior including memory corruption, invalid memory access patterns, and ultimately system instability. The nature of integer overflows in kernel space makes them particularly dangerous as they can potentially be leveraged for privilege escalation or more sophisticated attacks if combined with other vulnerabilities. These issues fall under the CWE-190 category of Integer Overflow or Wraparound, which is a well-documented weakness in software security that affects numerous system components.
The operational impact of CVE-2014-4656 extends beyond simple denial of service conditions to potentially compromise the entire audio subsystem of affected Linux systems. Local attackers who can access the /dev/snd/controlCX devices can trigger these overflows to cause the sound subsystem to crash, resulting in complete audio functionality loss until the system is rebooted or the affected kernel modules are unloaded. This vulnerability is particularly concerning in multi-user environments where audio access is granted to regular users, as it provides a straightforward path for malicious users to disrupt system services. The attack requires minimal privileges and can be executed repeatedly, making it a persistent threat to system availability. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1499.001 which involves network denial of service attacks, though in this case it operates at the kernel level rather than network level. The vulnerability demonstrates how seemingly minor flaws in kernel subsystems can have significant operational consequences.
Mitigation strategies for CVE-2014-4656 focus primarily on patching the affected kernel versions with updates that include proper integer bounds checking and overflow prevention mechanisms. System administrators should immediately upgrade to kernel versions 3.15.2 or later where these vulnerabilities have been addressed through proper input validation and overflow protection in the ALSA control implementation. Additionally, access controls for /dev/snd/controlCX devices should be reviewed and restricted to minimize the attack surface, though this approach provides only partial protection as the vulnerability exists within kernel code itself. Organizations should implement comprehensive monitoring to detect unusual patterns in audio subsystem behavior that might indicate exploitation attempts. The fix implemented in the patched kernels addresses the root cause by ensuring proper validation of index and numid values before they are processed, preventing the integer overflow conditions that led to system instability. This vulnerability underscores the importance of kernel security reviews and proper input validation in critical system components, particularly those that handle user-provided data in privileged contexts.