CVE-2026-52946: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-52946 is a deadlock vulnerability in the Linux kernel's fs/fcntl subsystem, specifically in the FASYNC signal delivery path (send_sigio() and send_sigurg()). The flaw arises from an unsafe lock ordering between SOFTIRQ-safe and SOFTIRQ-unsafe contexts when signaling process groups, which can result in a system deadlock and denial of service. It affects the Linux kernel from version 2.6.12 through multiple stable branches, with fixes available in versions 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13, 7.1.1, and 7.2-rc1. The vulnerability was published on June 24, 2026, and carries a CVSS v3.1 base score of 7.5 (High) (Feedly).

The root cause is an improper lock ordering (CWE-667: Improper Locking) in the Linux kernel's FASYNC process group signaling path. When FASYNC is configured for a process group (PIDTYPE_PGID), both send_sigio() and send_sigurg() acquire read_lock(&tasklist_lock) to traverse the task list. These functions are frequently invoked from softirq context — send_sigio() via input_inject_event → kill_fasync, and send_sigurg() via tcp_check_urg → sk_send_sigurg (NET_RX_SOFTIRQ). The deadlock scenario unfolds as follows: CPU 0 holds read_lock(&tasklist_lock) in do_wait(); CPU 1 attempts write_lock(&tasklist_lock) in fork() or exit(), spinning and blocking all new readers; CPU 0 is then interrupted by a softirq (e.g., a TCP URG packet), which attempts to re-acquire read_lock(&tasklist_lock), causing a deadlock. The fix replaces tasklist_lock with rcu_read_lock() in the process group signaling path, since PID hashing and do_each_pid_task() traversals are already RCU-protected (Feedly).

Successful exploitation causes a kernel deadlock, resulting in a complete denial of service for the affected system — the machine becomes unresponsive and requires a reboot. There is no confidentiality or integrity impact; the vulnerability is limited to availability. The attack can be triggered remotely without authentication (e.g., by sending a TCP URG packet to a system with FASYNC-configured process groups), making it a potential remote denial-of-service vector (Feedly).

The Linux kernel maintainers have released patches across all affected stable branches. Users should update to the following fixed versions or later: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13, or 7.1.1. Downstream distributions including Amazon Linux 2023 (ALAS2023-2026-1924), Amazon Linux 2 kernel 5.10 (ALAS2KERNEL-5.10-2026-124), openSUSE, and Debian 11 have also issued security updates. Administrators should apply the relevant kernel update for their distribution as soon as possible and reboot to activate the fix (Feedly, Amazon Linux Advisory, openSUSE Advisory).