CVE-2026-68176 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing: Fix mmiotrace possible NULL dereferencing of hiter->dev
If the mmio_pipe_open() fails to find a PCI device, the hiter->dev will be assigned to NULL. The mmiotrace read() function dereferences the hiter->dev if hiter exists.
Change the test of the read to not only check hiter being NULL, but also the hiter->dev before dereferencing it.
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability resides within the Linux kernel's tracing subsystem, specifically affecting the mmiotrace functionality that monitors memory-mapped I/O operations. The issue manifests as a potential null pointer dereference during the read operation of mmio trace data, representing a critical security flaw that could lead to system instability or privilege escalation. The vulnerability stems from inadequate validation checks within the kernel's device enumeration and tracing mechanisms.
The technical root cause involves the mmio_pipe_open() function which attempts to locate PCI devices for monitoring purposes. When this lookup fails to find a matching device, the hiter->dev field is assigned a NULL value, creating a dangerous condition where subsequent code paths may attempt to dereference this null pointer. The mmiotrace read() function operates under the assumption that if hiter exists, then hiter->dev must also be valid, failing to account for the possibility that device lookup could have failed. This violates fundamental defensive programming principles and creates a classic null pointer dereference vulnerability.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling malicious actors to exploit the kernel's tracing subsystem for privilege escalation or denial of service attacks. Attackers could craft specific inputs or trigger conditions that force the kernel into the problematic code path, leading to system panics or unauthorized access to kernel memory spaces. The vulnerability affects systems running Linux kernels with mmiotrace functionality enabled, particularly those handling complex PCI device configurations where device enumeration might legitimately fail.
This issue aligns with CWE-476 which specifically addresses null pointer dereference conditions in software systems. The vulnerability also relates to ATT&CK technique T1059.003 for executing malicious code through kernel-level vulnerabilities and T1499.004 for system disruption via kernel exploits. The fix implements proper null checking before dereferencing the hiter->dev pointer, ensuring that both hiter and hiter->dev are validated as non-null before proceeding with the read operation. This defensive programming approach prevents the null pointer dereference while maintaining the intended functionality of the tracing subsystem.
The resolution involves modifying the validation logic in the mmiotrace read() function to explicitly check both hiter and hiter->dev for null values before attempting any dereference operations. This change ensures that the kernel's tracing subsystem properly handles device lookup failures gracefully without crashing or exposing exploitable conditions. The fix represents a standard mitigation strategy for preventing null pointer dereferences in kernel space code, aligning with established security practices for kernel vulnerability remediation and maintaining system stability under error conditions while preserving the intended monitoring capabilities of the mmiotrace functionality.