CVE-2026-68177 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing: Delay module ref count for "enable_event" trigger
Triggers are now delayed from freeing, but can still be triggered until after the RCU grace period has ended. The freeing of the enable_event data is put into the private_data_free() callback, but the put of the module refcount is done immediately.
It is possible that if a module is removed that has an event that would enable (or disable) it is still active, it can read the data of the module after it is removed causing a use-after-free bug.
Move the trace_event_put_ref() that releases the module into the delayed callback so that the module can not be removed until any reference to its events are finished.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability identified in the Linux kernel relates to improper handling of module reference counts during tracing operations, specifically within the enable_event trigger mechanism. This flaw exists in the kernel's tracing subsystem where triggers associated with trace events are managed through a complex reference counting system that involves both immediate and delayed cleanup operations. The issue stems from a fundamental timing problem in how module references are released when trace events are being processed or removed from memory.
The technical implementation flaw occurs because the tracing subsystem employs two distinct callbacks for cleaning up trace event data: one immediate callback that handles the initial freeing of enable_event data structures, and another delayed callback that manages the private_data_free() operations. The module reference count release operation is executed immediately upon trigger removal, while the actual cleanup of trace event data is deferred to a later point in time through the private_data_free() callback. This asynchronous behavior creates a window where a module can be unloaded from memory while still having active references to its trace event data structures.
This vulnerability falls under the category of use-after-free bugs, which are classified as CWE-416 and represent a critical class of memory safety issues that can lead to arbitrary code execution or system crashes. The flaw allows for potential privilege escalation attacks when an attacker can manipulate module loading and unloading sequences to trigger the race condition between reference counting and data cleanup operations. The vulnerability is particularly concerning because it operates at kernel level where such memory corruption issues can compromise entire system security.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a fundamental flaw in the kernel's module management and reference counting mechanisms. When a module containing trace events is unloaded while those events are still active or referenced, the system may attempt to access freed memory locations, leading to unpredictable behavior including potential kernel panics, data corruption, or exploitation for privilege escalation attacks. The timing aspect of this vulnerability means that even brief periods of module unloading during active tracing operations can create exploitable conditions.
Mitigation strategies for this vulnerability require modifications to the kernel's tracing subsystem to ensure proper synchronization between module reference counting and trace event cleanup operations. The solution involves moving the trace_event_put_ref() operation, which releases module references, into the delayed callback mechanism rather than executing it immediately during trigger removal. This ensures that modules cannot be unloaded until all references to their trace events have been fully processed and cleaned up, eliminating the race condition that leads to use-after-free conditions. The fix aligns with established security practices for managing kernel-level reference counting and memory cleanup operations, ensuring that resource management follows proper temporal ordering principles as recommended in secure coding standards.
The vulnerability demonstrates patterns commonly associated with ATT&CK technique T1068 which involves privilege escalation through local exploitation of kernel vulnerabilities. Systems running affected kernel versions are at risk of attackers exploiting this timing race condition to gain elevated privileges or cause system instability, making prompt patching essential for maintaining system security. The fix represents a defensive programming approach that prevents the specific class of use-after-free vulnerabilities by ensuring proper resource lifetime management in kernel tracing subsystems, thereby reducing attack surface and improving overall system resilience against memory corruption attacks.