CVE-2026-98263 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
ASoC: codecs: rt712-sdca-dmic: fix uninitialized stream_config->type
stream_config is not initialized before being passed to sdw_stream_add_slave(). The type field may contain garbage and is later copied to stream->type by sdw_config_stream().
Zero-initialize stream_config so type defaults to SDW_STREAM_PCM.
While at it, use snd_sdw_params_to_config() helper instead of open-coding the same logic.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel audio subsystem contains a critical initialization flaw within the Realtek RT712 codec driver for SoundWire Digital Microphone interfaces. This vulnerability arises from improper handling of local data structures during stream configuration, specifically involving an uninitialized variable that leads to undefined behavior and potential security risks. The core issue is located in the sdw_stream_add_slave function call path where a structure named stream_config is utilized but not properly initialized prior to use. In C programming, local variables are allocated on the stack without automatic zeroing unless explicitly specified or declared as static. Consequently, any fields within this structure that are not explicitly set by subsequent logic will retain whatever data previously occupied those memory locations from other function calls or system operations.
The specific technical flaw centers on the type field of the stream_config structure. This field is intended to define the nature of the audio stream being configured, such as whether it carries PCM audio data or other formats. Because the entire stream_config structure was not zero-initialized before being passed to sdw_stream_add_slave(), the type field contains garbage values derived from prior stack usage. The function sdw_config_stream subsequently copies this uninitialized value into the persistent stream->type member of the sound card driver state. This action effectively propagates unpredictable, arbitrary data into a core component that dictates how audio streams are processed and managed by the kernel's sound architecture.
From an operational perspective, relying on garbage values for critical configuration parameters can lead to severe system instability. If the uninitialized type field contains a value that does not correspond to any valid stream type defined in the SoundWire specification or Linux kernel enums, it may cause downstream functions to behave incorrectly. This could manifest as audio distortion, complete failure of sound output or input on devices utilizing this codec, or more critically, logic errors within the driver's state machine. In worst-case scenarios involving complex memory interactions and subsequent processing based on these invalid types, such undefined behavior can potentially be exploited for local privilege escalation if an attacker can influence the stack contents prior to triggering the vulnerability through audio device initialization sequences.
The remediation strategy implemented in this fix addresses both the immediate symptom and underlying code quality issues. The primary correction involves zero-initializing the stream_config structure at its declaration point using standard C syntax such as struct sdw_stream_config stream_config = { 0 }. This ensures that all fields, including type, start with a known safe default value rather than random stack data. By doing so, if no explicit assignment occurs later in the logic flow, the field defaults to SDW_STREAM_PCM which is generally a safe baseline for audio streams and prevents the propagation of uninitialized memory contents into critical driver structures.
Furthermore, the fix improves code maintainability and reduces future risk by refactoring how stream parameters are derived from hardware configuration settings. Instead of manually implementing or open-coding the logic required to map sound card parameters to SoundWire stream configurations, developers now utilize the snd_sdw_params_to_config helper function. This abstraction layer not only simplifies the driver code but also centralizes the complex mapping logic in a well-tested utility routine. Using standardized helpers reduces the likelihood of similar initialization errors or logical mismatches occurring elsewhere in the audio subsystem and aligns the driver with broader kernel coding standards for consistency and reliability across different hardware implementations.
This vulnerability is categorized under CWE-457 which describes the use of an uninitialized variable, a common source of bugs in systems programming languages like C where manual memory management is required. The potential impact on system integrity places it within the scope of ATT&CK technique T1068 related to exploitation for privilege escalation if the resulting instability can be leveraged to crash security mechanisms or trigger kernel panics that bypass standard protections. Mitigation requires applying the specific patch provided by Linux distribution maintainers which updates the rt712-sdca-dmic driver module. System administrators should ensure their kernels are updated to versions containing this fix, particularly on systems relying on Realtek RT712 codecs for audio input or output functionality. Regular auditing of kernel code for proper variable initialization practices remains essential to prevent similar vulnerabilities in other subsystems that handle hardware configuration and state management.