CVE-2026-23129 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
dpll: Prevent duplicate registrations
Modify the internal registration helpers dpll_xa_ref_{dpll,pin}_add()
to reject duplicate registration attempts.
Previously, if a caller attempted to register the same pin multiple times (with the same ops, priv, and cookie) on the same device, the core silently increments the reference count and return success. This behavior is incorrect because if the caller makes these duplicate registrations then for the first one dpll_pin_registration is allocated and for others the associated dpll_pin_ref.refcount is incremented. During the first unregistration the associated dpll_pin_registration is freed and for others WARN is fired.
Fix this by updating the logic to return `-EEXIST` if a matching registration is found to enforce a strict "register once" policy.
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Analysis
by VulDB Data Team • 03/19/2026
The vulnerability identified as CVE-2026-23129 resides within the Linux kernel's digital phase-locked loop subsystem, specifically affecting the dpll framework's registration mechanisms. This issue represents a critical flaw in resource management and state tracking that can lead to unpredictable behavior and potential system instability. The vulnerability impacts devices that utilize digital phase-locked loop functionality for clock synchronization and timing control, particularly in embedded systems, network infrastructure, and industrial control environments where precise timing is essential. The flaw manifests in the internal registration helpers dpll_xa_ref_{dpll,pin}_add() which are responsible for managing references to digital phase-locked loop components and their associated pins.
The technical root cause of this vulnerability stems from improper duplicate detection logic within the registration process. When a caller attempts to register the same pin multiple times using identical operations, private data, and cookie values on the same device, the kernel's current implementation silently increments a reference count without proper validation. This incorrect behavior creates a fundamental inconsistency in the registration state management system. During the initial registration, a dpll_pin_registration structure is properly allocated to track the pin's state and configuration. However, subsequent duplicate registration attempts only increment the dpll_pin_ref.refcount field without creating additional registration structures. This asymmetry in the registration and unregistration processes creates a dangerous condition where the first unregistration properly frees the allocated memory structure while subsequent unregistrations trigger kernel warnings due to the inconsistent state management.
The operational impact of this vulnerability extends beyond simple resource management issues to potentially compromise system stability and reliability. When duplicate registrations occur, the system's internal state becomes inconsistent, leading to potential memory corruption, kernel panics, or unexpected behavior during cleanup operations. This flaw particularly affects systems that dynamically register and unregister phase-locked loop components during runtime operations, such as network switches, routers, and embedded systems that adjust clock frequencies based on system load or environmental conditions. The vulnerability creates a race condition scenario where the system may attempt to free memory structures that have already been released, potentially leading to use-after-free conditions that attackers could exploit to gain unauthorized access or cause system crashes. The issue aligns with CWE-362, which addresses concurrent execution using improper synchronization, and represents a classic example of improper resource management in kernel space.
The fix implemented for CVE-2026-23129 modifies the registration logic to enforce a strict "register once" policy by returning -EEXIST when a matching registration is detected. This approach eliminates the ambiguous state management that previously existed and ensures that each pin can only be registered once within a given device context. The solution prevents the silent increment of reference counts for duplicate registrations and instead explicitly rejects subsequent attempts to register identical components. This change brings the kernel's behavior in line with standard resource management practices and aligns with the ATT&CK framework's defensive techniques related to system hardening and resource management. The mitigation approach ensures that all registration operations maintain consistent state throughout the system's lifecycle, preventing the cascade of errors that could occur during cleanup operations and providing a more predictable and secure environment for systems utilizing digital phase-locked loop functionality. The fix also improves the overall robustness of the kernel's device management subsystem by eliminating potential points of failure in the registration and unregistration processes.