CVE-2025-38135 in Linux
Summary
by MITRE • 07/03/2025
In the Linux kernel, the following vulnerability has been resolved:
serial: Fix potential null-ptr-deref in mlb_usio_probe()
devm_ioremap() can return NULL on error. Currently, mlb_usio_probe() does not check for this case, which could result in a NULL pointer dereference.
Add NULL check after devm_ioremap() to prevent this issue.
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Analysis
by VulDB Data Team • 04/18/2026
The vulnerability identified as CVE-2025-38135 represents a critical null pointer dereference flaw within the Linux kernel's serial communication subsystem, specifically affecting the mlb_usio_probe() function. This issue resides in the kernel's handling of memory-mapped I/O resources for mobile low power bus devices, where the function fails to properly validate the return value from devm_ioremap() before proceeding with subsequent operations. The flaw manifests when the device memory mapping operation encounters an error condition, causing devm_ioremap() to return a NULL pointer instead of a valid memory address. This oversight creates a potential exploitation vector where malicious actors could trigger a kernel panic or system crash through carefully crafted device initialization sequences, directly impacting system stability and availability.
The technical implementation of this vulnerability stems from inadequate error handling within the device driver's probe function, which operates under the principles of the Common Weakness Enumeration framework as a CWE-476 Null Pointer Dereference. The mlb_usio_probe() function performs device resource allocation through devm_ioremap() without implementing proper validation checks, violating fundamental kernel programming best practices for resource management. When devm_ioremap() fails to map the required I/O memory region due to hardware issues, insufficient memory, or configuration errors, it returns NULL, but the subsequent code path does not account for this possibility. This error handling gap creates an execution path where the kernel attempts to dereference a NULL pointer, leading to immediate system termination or unpredictable behavior that can be exploited to cause denial of service conditions.
The operational impact of CVE-2025-38135 extends beyond simple system crashes, as it affects the reliability of serial communication subsystems in embedded devices, mobile platforms, and server environments where the mobile low power bus interface is utilized. The vulnerability can be triggered during normal device initialization procedures, making it particularly dangerous as it may occur during system boot processes or when hot-plugging serial devices. Attackers leveraging this flaw could potentially cause system-wide outages, especially in mission-critical infrastructure where device drivers are automatically loaded. The issue particularly affects systems running Linux kernel versions where the mlb_usio driver is active, including various embedded platforms, automotive systems, and mobile devices that utilize the mobile low power bus for communication protocols. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1490, as it enables system disruption through kernel-level manipulation, potentially allowing for privilege escalation or persistent access if combined with other vulnerabilities in the system.
The recommended mitigation strategy involves implementing a simple but crucial null pointer check immediately after the devm_ioremap() function call within the mlb_usio_probe() function. This remediation follows established kernel development practices and security guidelines for preventing null pointer dereferences. The fix requires adding a conditional check to verify that the return value from devm_ioremap() is not NULL before proceeding with any operations that depend on the mapped memory region. This approach aligns with the principle of defensive programming and adheres to the Linux kernel's coding standards that emphasize robust error handling. System administrators should prioritize applying the kernel patch that implements this check, particularly in environments where the affected device drivers are actively used, as the vulnerability presents a straightforward exploitation path with significant impact potential. Organizations should also consider implementing monitoring for unusual system crashes or device initialization failures that might indicate exploitation attempts, as the vulnerability's effects are immediately visible through kernel log analysis and system stability metrics.