CVE-2026-98308 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: hda: trace PCM open only after assigning a stream
Stream assignment can fail when hardware streams are exhausted. Move the tracepoint after the NULL check because its payload accesses the assigned stream tag.
Detected by static analysis and reviewed with AI-assisted source auditing.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem, specifically within the High Definition Audio driver component known as hda, contained a logic error related to the ordering of operations during PCM stream initialization. This vulnerability arises from an improper sequence in handling hardware resource allocation and diagnostic tracing. When a user-space application attempts to open a new audio playback or capture device via the ALSA interface, the kernel must allocate a corresponding hardware stream from a finite pool of available resources managed by the HDA codec driver. If all hardware streams are currently occupied by other processes, this allocation process fails, resulting in a NULL pointer being returned for the newly requested stream structure rather than a valid memory address.
The technical flaw lies in the placement of a tracepoint invocation within the initialization code path. Prior to the fix, the kernel attempted to log diagnostic information about the PCM open event before verifying whether the hardware stream assignment had succeeded. The payload of this specific tracepoint includes accessing fields from the assigned stream tag structure to record details such as the stream ID or state. Because the NULL check for the stream pointer occurred after the tracepoint execution in the original code, a failed allocation would result in the tracing infrastructure attempting to dereference a NULL pointer. This constitutes an out-of-bounds read or null pointer dereference vulnerability that can lead to a kernel panic, effectively causing a denial of service against the entire system by crashing the operating kernel.
From a security and standards perspective, this issue aligns with CWE-476, which describes a NULL Pointer Dereference. The root cause is classified under CWE-391, Unchecked Error Condition, as the code failed to validate the success of an operation before proceeding with dependent actions that rely on the result's validity. In terms of adversarial tactics and defensive mapping, this vulnerability does not typically allow for remote code execution or privilege escalation in its default state but represents a stability risk exploitable through local denial-of-service attacks. It maps loosely to ATT&CK technique T1499, Endpoint Denial of Service, specifically under the sub-category of resource exhaustion leading to system instability. While an attacker would need local access and sufficient privileges to trigger multiple concurrent audio stream openings to exhaust hardware resources, the vulnerability highlights a critical lack of defensive programming practices in kernel-level driver code where input validation is paramount.
The operational impact of this flaw is primarily centered on system reliability rather than data confidentiality or integrity. A successful exploitation requires an attacker to open enough PCM streams simultaneously to exhaust the available hardware stream slots provided by the HDA codec. Once exhausted, any subsequent attempt to access audio devices would trigger the NULL pointer dereference during the tracing phase, causing an immediate kernel oops and a system reboot on most configurations. This disrupts all services running on the host, including critical infrastructure that may rely on stable uptime for real-time processing or continuous monitoring tasks. The vulnerability was detected through static analysis tools designed to identify potential null-pointer accesses in control flow paths, followed by AI-assisted source auditing which helped confirm the logical sequence error without requiring dynamic exploitation testing.
Mitigation strategies involve applying the upstream kernel patch that reorders the code execution path. By moving the tracepoint invocation to occur only after a successful NULL check of the assigned stream pointer, the driver ensures that diagnostic logging is performed exclusively on valid data structures. System administrators should ensure their Linux kernels are updated to versions containing this fix. For environments where immediate patching is not feasible, mitigating controls include limiting concurrent audio application usage through resource limits or cgroups, although this is a less robust defense than addressing the underlying code defect. The resolution reinforces best practices in kernel development by ensuring that side effects such as logging do precede critical validation checks unless those side effects are guaranteed to be safe under all execution paths, including error conditions.