CVE-2025-68734 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
isdn: mISDN: hfcsusb: fix memory leak in hfcsusb_probe()
In hfcsusb_probe(), the memory allocated for ctrl_urb gets leaked when setup_instance() fails with an error code. Fix that by freeing the urb before freeing the hw structure. Also change the error paths to use the goto ladder style.
Compile tested only. Issue found using a prototype static analysis tool.
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Analysis
by VulDB Data Team • 12/29/2025
The vulnerability identified as CVE-2025-68734 represents a memory leak condition within the Linux kernel's isdn subsystem, specifically affecting the mISDN framework's hfcsusb driver implementation. This flaw occurs during the device probe phase when the kernel attempts to initialize USB-based ISDN hardware interfaces. The issue manifests when the setup_instance() function fails to properly configure the hardware instance, leaving allocated memory resources unreleased. The root cause stems from improper resource management within the error handling path of the hfcsusb_probe() function, where the control urb structure allocated for USB communication remains in memory even when the initialization process encounters failures. This memory leak represents a classic resource management vulnerability that can accumulate over time, potentially leading to system instability or performance degradation. The vulnerability impacts systems utilizing USB-based ISDN hardware interfaces through the mISDN framework, which provides support for various ISDN protocols and hardware configurations in Linux environments.
The technical implementation of this vulnerability involves the hfcsusb_probe() function within the mISDN subsystem that manages USB communication for ISDN hardware devices. When setup_instance() fails to initialize the hardware configuration properly, the function fails to execute the necessary cleanup operations to release the previously allocated ctrl_urb memory structure. This memory leak occurs because the error handling code path does not properly free the urb structure before proceeding to clean up the hardware structure, creating a dangling reference to allocated memory. The improper resource management follows a common pattern where error handling logic fails to maintain proper cleanup order, leading to memory consumption that grows with each failed initialization attempt. The vulnerability demonstrates poor adherence to defensive programming practices and proper resource management protocols that should be implemented in kernel space drivers to prevent resource exhaustion. This type of memory leak directly relates to CWE-401, which specifically addresses memory leaks in software systems, and represents a failure to properly implement the principle of resource acquisition is initialization.
The operational impact of this vulnerability extends beyond simple memory consumption issues to potentially affect system stability and resource availability in production environments. While the leak may appear minor on individual system instances, repeated failed probe attempts can accumulate memory consumption over time, particularly in systems with high device enumeration activity or those experiencing frequent hardware connection issues. The vulnerability is particularly concerning in embedded systems or server environments where memory resources are constrained and system reliability is paramount. The memory leak can contribute to gradual performance degradation, increased garbage collection pressure, or even system crashes in extreme scenarios where memory exhaustion occurs. Additionally, the presence of such leaks in kernel space components can create indirect security implications by potentially enabling resource exhaustion attacks or by making systems more susceptible to other vulnerabilities that exploit memory corruption patterns. The vulnerability affects the broader mISDN subsystem and impacts any application or service that relies on proper USB ISDN hardware initialization and management.
The mitigation strategy for CVE-2025-68734 requires implementing proper error handling and resource cleanup procedures within the hfcsusb_probe() function. The fix involves restructuring the error paths to utilize a goto ladder style implementation that ensures all allocated resources are properly freed before function exit, specifically addressing the sequence where ctrl_urb memory must be released before the hw structure. This approach follows established kernel development practices and aligns with the principle of defensive programming in kernel space code where resource management must be robust against all error conditions. The solution requires careful attention to the cleanup order, ensuring that memory allocated for USB communication structures is freed before higher-level hardware structures are destroyed. The implementation should also include comprehensive testing of error paths to verify that all potential failure scenarios properly release resources. System administrators should monitor for memory usage patterns in environments with USB ISDN hardware and ensure timely application of kernel updates containing the fix. The fix addresses fundamental issues in the ATT&CK framework's resource exhaustion categories and demonstrates proper implementation of the kernel's memory management subsystem. The vulnerability resolution should be prioritized in security update cycles, particularly in environments where ISDN hardware is actively used or where resource constraints are a concern.