CVE-2025-21756: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-21756 affects the Linux kernel's vsock (Virtual Socket) implementation. The vulnerability was discovered and disclosed on February 26, 2025, and involves a use-after-free issue in the socket binding mechanism. The issue occurs during socket destruction and transport reassignment processes in the vsock subsystem (NVD).

The vulnerability stems from improper handling of socket bindings during transport reassignment. The issue manifests in a sequence where: 1) vsockcreate() sets refcnt=1 and calls vsockinsertunbound() (refcnt=2), 2) transport->release() calls vsockremovebound() without verifying if the socket was bound and moved to bound list (refcnt=1), and 3) vsockbind() assumes the socket is in unbound list and calls _vsockremove_bound() leading to a use-after-free condition. The vulnerability has been assigned a CVSS v3.1 Base Score of 7.8 (HIGH) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (CISA-ADP).

The vulnerability can lead to use-after-free conditions in the kernel's vsock subsystem, potentially resulting in system crashes, memory corruption, or privilege escalation. The issue affects systems using virtual socket functionality in the Linux kernel (NVD).

The issue has been fixed in the Linux kernel through a patch that preserves socket bindings until socket destruction. The fix modifies the vsockremovesock() function to check for SOCKDEAD flag before removing bindings and adjusts the order of operations in _vsock_release() (Kernel Git).