CVE-2026-98690 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
thunderbolt: Fix domain reference leak when DPRX read is canceled
tb_tunnel_one_dp() takes a domain reference which is only dropped once tb_dp_tunnel_active() has run on the work queue. If that work is cancelled that reference is leaked. Since commit f5cc545f5969 ("thunderbolt: Wait for tb_domain_release() to complete when driver is removed") instead of just leaking memory this now also blocks in the completion wait forever when unbinding the driver.
This can be triggered whenever a DP tunnel is torn down before the DPRX read has completed, e.g. by unplugging within the timeout, and then unbinding the driver.
That reference only exists to keep the domain around while the DPRX work is scheduled so let the work itself own it: take it in tb_dp_dprx_start() and drop it in both places that end the work. Get/put are then paired inside the same file and it doesn't matter anymore if the callback ever runs.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability identified as a domain reference leak within the Linux kernel Thunderbolt subsystem represents a critical resource management flaw affecting system stability during driver unbinding operations. The core issue resides in the tb_tunnel_one_dp function, which acquires a reference to the thunderbolt domain object to ensure its persistence while DisplayPort tunneling activities are scheduled for execution. Under normal operational conditions, this reference is intended to be released only after the tb_dp_tunnel_active callback has successfully executed within the kernel work queue context. However, when the associated work item is cancelled prior to completion—such as during a rapid disconnection event where a display port cable is unplugged before the read timeout expires—the code path fails to release this acquired reference. This oversight results in a persistent memory leak that accumulates with each such cancellation event.
The severity of this vulnerability escalates significantly due to changes introduced in commit f5cc545f5969, which modified the driver removal process to wait for tb_domain_release to complete before finalizing unbinding. Because the leaked reference prevents the domain object from reaching a zero-reference count, the release function never completes its execution. Consequently, when an administrator or system component attempts to unload the Thunderbolt driver while such pending cancellations exist, the kernel enters an infinite blocking state within the completion wait mechanism. This effectively causes a denial of service by hanging the unbinding process and potentially freezing related subsystem operations until manual intervention is required.
From a technical classification perspective, this flaw aligns with CWE-401, which describes missing release of memory after successful allocation, specifically manifesting as a reference count leak in object-oriented kernel structures. The attack vector involves triggering specific race conditions or rapid hardware state changes that cause work queue cancellation during active tunnel teardown procedures. This behavior is consistent with ATT&CK technique T1529, System Shutdown/Reboot Obfuscation via resource exhaustion, although the primary impact here is system instability rather than malicious obfuscation. The vulnerability highlights a common pitfall in kernel driver development where reference counting logic must account for all exit paths, including error handling and cancellation scenarios, to maintain object lifecycle integrity.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that corrects this reference counting imbalance. The fix restructures the ownership of the domain reference by transferring it from the tunneling setup phase directly into the tb_dp_dprx_start function. This ensures that the work item itself owns the reference, allowing for a symmetric get and put operation within the same file scope regardless of whether the callback executes fully or is cancelled prematurely. By dropping the reference in both termination paths of the work execution, the domain object can be properly released even if the DPRX read is interrupted. System administrators should ensure their kernels are updated to versions containing this fix to prevent driver unbinding hangs and associated resource leaks during Thunderbolt device management operations.