CVE-2025-71194: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-71194 is a deadlock vulnerability in the Linux kernel's Btrfs filesystem subsystem, specifically in the wait_current_trans() function called during start_transaction(). The flaw occurs because wait_current_trans() waits for a blocked transaction without considering whether the given transaction type actually needs to wait for that particular transaction state, as defined by the btrfs_blocked_trans_types[] array. This can result in a kernel deadlock involving two transactions and pending ordered extents. The vulnerability was published on February 4, 2026, and affects the Linux kernel across multiple stable branches. Feedly estimates the severity as Medium, with an EPSS score of 0.000180 (Feedly).

The root cause is a logic omission (CWE-667: Improper Locking) in the Btrfs transaction handling code. When wait_current_trans() is invoked, it unconditionally waits if it detects a blocked transaction state, ignoring the btrfs_blocked_trans_types[] array that specifies which transaction join types should block on which states. The deadlock scenario unfolds as follows: (1) Transaction A enters TRANS_STATE_COMMIT_DOING; (2) an ordered extent worker calls start_transaction() with TRANS_JOIN, which returns -EBUSY; (3) Transaction A completes and a new Transaction B is created; (4) the ordered extent is added to Transaction B's pending list; (5) Transaction B immediately enters TRANS_STATE_COMMIT_START; (6) the worker reaches wait_current_trans(), sees Transaction B in a blocked state, and waits unconditionally — but TRANS_JOIN should not block on TRANS_STATE_COMMIT_START, causing a deadlock. The fix adds the missing transaction-type check to wait_current_trans() to align its behavior with the btrfs_blocked_trans_types[] definitions (Feedly).

Successful triggering of this vulnerability causes a kernel deadlock in the Btrfs filesystem subsystem, resulting in a denial of service (system hang or unresponsive filesystem). The impact is limited to availability — there is no evidence of confidentiality or integrity compromise. Systems using Btrfs as their filesystem and running affected Linux kernel versions are at risk, particularly workloads with concurrent transaction activity and ordered extent processing (Feedly).

The Linux kernel maintainers have released patches addressing this vulnerability across multiple stable branches, with fixes committed to the kernel stable tree (commits 8b0bb145d3bc, 9ac63333d600, 99da896614d1, 5037b342825d, d7b04b40ac8e). Downstream distributions including Ubuntu (USN-8162-1, USN-8180-1 through USN-8180-6, USN-8186-1, USN-8188-1, USN-8275-1, USN-8278-1, USN-8289-1, USN-8296-1, USN-8297-1), Amazon Linux 2 (ALAS2KERNEL-5.15-2026-098, ALAS2KERNEL-5.15-2026-099), SUSE (SUSE-2026-0962-1), and Oracle Enterprise Linux have issued kernel updates. Users should update to the latest patched kernel version provided by their distribution. No configuration-based workaround is available; the only remediation is applying the kernel patch (Ubuntu USN-8162-1, Amazon ALAS).