CVE-2025-40002: 
Linux Debian vulnerability analysis and mitigation

A use-after-free vulnerability has been discovered in the Linux kernel's thunderbolt subsystem, identified as CVE-2025-40002. The vulnerability was disclosed on October 18, 2025, affecting the thunderbolt driver's DisplayPort functionality. The issue exists in the tbdpdprx_work function where improper handling of delayed work items can lead to use-after-free scenarios (NVD).

The vulnerability stems from the reliance on canceldelayedwork() in tbdpdprxstop(), which does not ensure that the delayed work item tunnel->dprxwork has fully completed if it was already running. This can result in a race condition where tbtunnel is deallocated by tbtunnelput(), while tunnel->dprxwork remains active and attempts to dereference tbtunnel in tbdpdprxwork(). The issue cannot be fixed by using canceldelayedworksync() as it would introduce a deadlock due to both tbdpdprxwork() and the cleanup path acquiring tb->lock (NVD).

The vulnerability can lead to use-after-free scenarios in the Linux kernel's thunderbolt subsystem, potentially resulting in system crashes or memory corruption. This could affect systems utilizing Thunderbolt DisplayPort functionality (NVD).

The issue has been resolved by implementing proper reference counting: if canceldelayedwork() returns true (work is pending), the reference is released in the stop function; if it returns false (work is executing or already completed), the reference is released in the delayed work function itself. This ensures the tb_tunnel remains valid during work item execution while preventing memory leaks (NVD).