CVE-2025-68264: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-68264 is a race condition vulnerability in the Linux kernel's ext4 filesystem inline data handling that can cause a kernel panic (BUG_ON crash). The flaw exists in fs/ext4/inline.c where the cached ei->i_inline_size value can become stale between an initial size check and its use in ext4_update_inline_data() or ext4_create_inline_data(), due to concurrent xattr operations modifying i_inline_size before the xattr lock is acquired. It was published on December 16, 2025, and affects multiple Linux kernel stable branches. Feedly estimates the severity as Medium, with an EPSS score of 0.000180 (Feedly).

The root cause is a time-of-check to time-of-use (TOCTOU) race condition (CWE-362) in the ext4 inline data write path. The sequence is: (1) ext4_get_max_inline_size() reads i_inline_size (e.g., 60 bytes) and the size check passes; (2) a concurrent thread adds an xattr, reducing i_inline_size to 40 bytes; (3) ext4_write_lock_xattr() acquires the lock; (4) ext4_update_inline_data() proceeds using the stale value of 60, attempting to write 50 bytes into only 40 bytes of available space; (5) the assertion BUG_ON(pos + len > EXT4_I(inode)->i_inline_size) in ext4_write_inline_data() at inline.c:1331 triggers a kernel panic. The fix recalculates i_inline_size via ext4_find_inline_data_nolock() immediately after acquiring xattr_sem, ensuring consistency. Patches are available across multiple stable kernel commits (Feedly).

Successful exploitation of this vulnerability results in a kernel BUG_ON panic, causing an immediate system crash and denial of service. The vulnerability is triggered locally by concurrent filesystem operations on ext4 volumes with inline data enabled, and does not directly expose confidentiality or allow privilege escalation. However, repeated triggering could be used to destabilize or crash affected Linux systems, impacting availability of any services running on them (Feedly).

• Logs: Kernel panic messages in /var/log/kern.log or dmesg output containing kernel BUG at fs/ext4/inline.c:1331! and BUG_ON(pos + len > EXT4_I(inode)->i_inline_size).
• System: Unexpected system reboots or kernel oops traces referencing ext4_write_inline_data, ext4_update_inline_data, or ext4_create_inline_data in the call stack.
• Process: Processes performing concurrent small file writes and xattr modifications on ext4 filesystems with inline data enabled immediately prior to a crash.

The fix has been backported to multiple Linux kernel stable branches via commits 43bf001f0fe4, 54ab81ae5f21, 58df743faf21, 89c2c41f0974, and 210ac60a86a3. Downstream distributions have released patches: Debian (linux 6.1.162-1, linux 5.10.249-1), Ubuntu (USN-8096-1/2/3/5, USN-8094-3/4/5, USN-8152-1, USN-8179-1/2/3/4, USN-8184-1, USN-8185-1/2, USN-8203-1, USN-8258-1, USN-8260-1, USN-8265-1), Amazon Linux 2 (ALAS2KERNEL-5.10-2026-113, ALAS2KERNEL-5.15-2026-098), and Oracle Linux. Users should update to the latest patched kernel version provided by their distribution. As a workaround, disabling ext4 inline data (mount option noinline_data) can prevent the race condition from occurring (Ubuntu USN-8096-1, Debian LTS, Amazon Linux).