CVE-2014-4655 in Android
Summary
by MITRE
The snd_ctl_elem_add function in sound/core/control.c in the ALSA control implementation in the Linux kernel before 3.15.2 does not properly maintain the user_ctl_count value, which allows local users to cause a denial of service (integer overflow and limit bypass) by leveraging /dev/snd/controlCX access for a large number of SNDRV_CTL_IOCTL_ELEM_REPLACE ioctl calls.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2014-4655 resides within the Advanced Linux Sound Architecture (ALSA) subsystem of the Linux kernel, specifically in the sound/core/control.c file. This flaw affects kernel versions prior to 3.15.2 and represents a critical security issue that can be exploited by local attackers with access to /dev/snd/controlCX devices. The vulnerability stems from improper handling of the user_ctl_count variable during control element operations, creating a pathway for malicious actors to manipulate kernel memory structures through legitimate audio control interfaces.
The technical root cause involves the snd_ctl_elem_add function's failure to properly validate and maintain the user_ctl_count value when processing SNDRV_CTL_IOCTL_ELEM_REPLACE ioctl commands. This oversight creates an integer overflow condition that allows attackers to bypass existing limit checks designed to prevent excessive control element creation. When a large number of these ioctl calls are made in sequence, the unchecked counter variable can wrap around to a small positive value or zero, effectively disabling the legitimate limit enforcement mechanisms. This behavior enables attackers to create an excessive number of control elements that can exhaust kernel resources or cause memory corruption.
The operational impact of this vulnerability manifests as a local denial of service condition that can severely impact system stability and audio functionality. Attackers can leverage this flaw to consume excessive kernel memory resources, potentially causing the system to become unresponsive or crash entirely. The vulnerability is particularly dangerous because it requires minimal privileges - only access to the /dev/snd/controlCX device files, which are typically accessible to regular users in many Linux distributions. This makes the attack surface broad and the exploitation relatively straightforward, as demonstrated by the fact that the vulnerability affects the core audio subsystem that many applications depend upon for proper operation.
The vulnerability maps directly to CWE-190, Integer Overflow or Wraparound, and CWE-129, Improper Validation of Array Index, which are both fundamental weaknesses in input validation and integer handling. From an ATT&CK perspective, this vulnerability aligns with T1068, Exploitation for Privilege Escalation, and T1499, Endpoint Termination, as it enables local users to cause system instability through kernel-level manipulation. The attack vector is particularly concerning because it operates at the kernel level, where the attacker's control is extensive and can potentially lead to more sophisticated attacks. The exploitability is enhanced by the fact that the vulnerability can be triggered through legitimate system interfaces, making it difficult to detect through traditional monitoring approaches.
Mitigation strategies for CVE-2014-4655 include applying the kernel patch released in version 3.15.2, which properly implements bounds checking for the user_ctl_count variable and prevents the integer overflow condition. System administrators should also implement proper access controls for audio device files, limiting access to only trusted users and processes. Additionally, monitoring for unusual patterns of ioctl calls to audio control devices can help detect potential exploitation attempts. The most effective long-term solution involves upgrading to kernel versions that contain the patched implementation, as the vulnerability fundamentally stems from a design flaw in the control element management system that was corrected in the subsequent kernel releases.