CVE-2022-50864: 
Linux Kernel vulnerability analysis and mitigation

CVE-2022-50864 is a shift-out-of-bounds vulnerability in the Linux kernel's nilfs2 filesystem driver. When the s_log_block_size field in nilfs2 superblock data is corrupted or set to an excessively large value, the init_nilfs() and load_nilfs() functions can trigger an undefined behavior shift operation (e.g., shift exponent 38973 for a 32-bit int), resulting in a UBSAN warning and potential kernel panic if panic_on_warn is enabled. The vulnerability was published on December 30, 2025, and affects the Linux kernel across multiple stable branches. It carries an estimated CVSS severity of Medium with an EPSS score of approximately 0.018% (Feedly, ENISA EUVD).

The root cause is improper input validation (CWE-1284: Improper Validation of Specified Quantity in Input) when reading the s_log_block_size field from the nilfs2 superblock during filesystem mount. If this field contains a maliciously crafted or corrupted value, the kernel performs a left bit-shift operation with an exponent far exceeding the valid range for a 32-bit integer, triggering undefined behavior detected by UBSAN. The fix introduces a new helper function that validates the block size exponent before use in init_nilfs() and load_nilfs(). Exploitation requires the ability to mount a crafted nilfs2 filesystem image, which typically requires local access or control over a storage device presented to the system (Feedly, ENISA EUVD).

Successful exploitation causes a UBSAN shift-out-of-bounds warning and, if panic_on_warn is set in the kernel configuration, a kernel panic leading to a denial of service (system crash). The primary impact is availability — an attacker who can mount a crafted nilfs2 image can crash the host kernel. There is no evidence of confidentiality or integrity impact beyond the system crash itself (Feedly).

The Linux kernel maintainers have released patches across multiple stable branches: Linux 5.10.163, 5.15.86, 6.0.16, 6.1.2, and 6.2. Administrators should update to these or later patched kernel versions. As a workaround, systems that do not require nilfs2 support can blacklist or disable the nilfs2 kernel module to prevent mounting of nilfs2 filesystems entirely (echo 'install nilfs2 /bin/true' >> /etc/modprobe.d/disable-nilfs2.conf). Restricting unprivileged users from mounting filesystems (e.g., via nosuid/nodev policies or disabling user_allow_other in FUSE) also reduces exposure (ENISA EUVD).