Linux Kernel F2FS Inline Extended Attribute Size Validation Bypass

CVE-2026-63815 is a validation bypass vulnerability in the Linux kernel's F2FS filesystem implementation that occurs when the flexible_inline_xattr feature is enabled. The vulnerability exists because do_read_inode() unconditionally loads the on-disk i_inline_xattr_size value without proper bounds checking, while sanity_check_inode() only validates this value when the FI_INLINE_XATTR flag is set. This allows inodes without the inline extended attributes flag to carry arbitrary inline attribute size values, potentially leading to memory corruption, information disclosure, or privilege escalation. The vulnerability affects Linux systems running vulnerable kernel versions with F2FS enabled and the flexible_inline_xattr feature active, impacting both direct users and those running containerized or virtualized environments on affected hosts.

Casky's platform, leveraging Claude AI's extended reasoning capabilities across 754 mapped security skills, would detect attack patterns associated with this vulnerability by analyzing kernel memory access anomalies and filesystem metadata inconsistencies. While MITRE ATT&ACK technique mappings are not yet available for this specific CVE, practitioners using Casky would identify suspicious patterns including: unauthorized memory access attempts targeting inode structures, unusual filesystem metadata modifications, and potential exploitation attempts that leverage the validation bypass to corrupt kernel memory. Security teams would see findings related to local privilege escalation attempts, memory safety violations, and filesystem integrity issues—enabling them to correlate these indicators with vulnerable kernel versions and implement targeted mitigations before exploitation occurs.