CVE-2026-96675 in Alsa-lib
Summary
by MITRE • 09/23/2026
alsa-lib through 1.2.16.1 contains a denial of service vulnerability in the multi PCM plugin that fails to validate sparse binding indices before array access. Attackers can supply a malicious ALSA configuration file with sparse bindings to trigger an out-of-bounds array read and assertion failure, causing the application to abort.
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Analysis
by VulDB Data Team • 09/23/2026
The Advanced Linux Sound Architecture (ALSA) library serves as a critical component in the Linux operating system ecosystem, providing applications with access to audio hardware through a standardized interface. Within this framework, the multi PCM plugin facilitates complex audio routing scenarios by allowing multiple sound cards or devices to be combined into a single logical device. This functionality is essential for professional audio workstations and systems requiring simultaneous output to different hardware endpoints. However, in versions of alsa-lib up to 1.2.16.1, a critical implementation flaw exists within the handling of sparse binding indices during this multi-device configuration process. The vulnerability stems from insufficient validation checks before accessing internal data structures that map these bindings, creating a pathway for memory corruption and application instability when processing maliciously crafted input configurations.
The technical root cause of this denial of service vulnerability lies in the failure to validate array bounds prior to access operations involving sparse binding indices. When an ALSA configuration file specifies multiple devices with non-contiguous or irregular index mappings, the library attempts to resolve these references by accessing internal arrays that store device-specific parameters and state information. The code path responsible for this resolution does not adequately verify whether the provided index falls within the valid range of allocated memory buffers. Consequently, if an attacker supplies a configuration file containing sparse bindings with indices exceeding the bounds of the underlying array, the application performs an out-of-bounds read operation. This access retrieves invalid or unintended data from adjacent memory locations, which subsequently triggers an assertion failure within the library's error handling mechanisms. The immediate operational result is the abrupt termination and abort of any process utilizing this ALSA configuration, effectively causing a denial of service for audio services on the affected system.
From a threat modeling perspective, this vulnerability aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. The exploitation vector is classified under Local Privilege Escalation in terms of impact scope if the audio service runs with elevated privileges, though primarily it manifests as a Denial of Service against local users who rely on stable audio processing capabilities. In the context of the MITRE ATT&CK framework, this behavior corresponds to techniques involving resource exhaustion or application crash via malformed input, often categorized under Impact categories such as Availability Loss. The requirement for an attacker to provide a specific configuration file implies that exploitation typically requires some level of access to modify system configurations or inject settings into applications using ALSA, making it more likely to be exploited in scenarios where users have write permissions to their own application directories or when combined with other vulnerabilities that allow arbitrary file creation.
The operational impact of this flaw is significant for environments relying on continuous audio processing, such as streaming servers, digital audio workstations, and embedded systems with persistent sound services. An attacker who can influence the ALSA configuration used by a target process can cause repeated crashes or instability in critical audio applications. This disruption can lead to data loss during recording sessions, interruption of live broadcasts, or general system unresponsiveness if core desktop environments depend on stable audio subsystems. While the vulnerability does not directly allow for arbitrary code execution due to its nature as an out-of-bounds read leading to assertion failure rather than write corruption, it severely compromises the reliability and availability of sound services. In high-security contexts where denial of service can be leveraged to distract security personnel or mask other malicious activities, this flaw presents a tangible risk vector that should not be overlooked in hardening strategies.
Mitigation for this vulnerability primarily involves upgrading alsa-lib to version 1.2.16.2 or later, where the developers have implemented proper bounds checking and validation logic for sparse binding indices before array access occurs. System administrators managing Linux distributions should ensure their package managers are configured to apply security updates promptly upon release of patched versions. For environments that cannot immediately update due to compatibility constraints, defensive configurations can be employed by restricting write permissions on ALSA configuration files such as alsa.conf or user-specific PCM config files in .asoundrc. By limiting which users or processes can modify these configuration files, the attack surface for injecting malicious sparse bindings is significantly reduced. Additionally, deploying application-level monitoring that detects abnormal termination of audio services may help identify exploitation attempts in real-time, allowing for rapid incident response and service restoration while permanent patches are applied across the infrastructure.