CVE-2026-63817
Received Received - Intake

F2FS Inode Validation Flaw in Linux Kernel

Publication date: 2026-07-19

Last updated on: 2026-07-19

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: f2fs: validate compress cache inode only when enabled F2FS_COMPRESS_INO() uses NM_I(sbi)->max_nid as the synthetic inode number for the compressed page cache inode. That inode only exists when the compress_cache mount option is enabled. When compress_cache is disabled, max_nid is outside the valid inode range. A corrupted directory entry that points to ino == max_nid should therefore be rejected by f2fs_check_nid_range(). However, is_meta_ino() currently treats F2FS_COMPRESS_INO() as a meta inode unconditionally, so f2fs_iget() bypasses do_read_inode() and its nid range check, and instantiates a fake internal inode instead. Gate the compressed cache inode case on COMPRESS_CACHE, matching f2fs_init_compress_inode(). With compress_cache disabled, ino == max_nid now follows the normal inode path and is rejected as an out-of-range nid.

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Meta Information

Published
2026-07-19
Last Modified
2026-07-19
Generated
2026-07-20
AI Q&A
2026-07-19
EPSS Evaluated
N/A
NVD
CVE-2026-63817
EUVD
EUVD-2026-45483

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves improper handling of the compressed page cache inode when the compress_cache mount option is disabled. The function F2FS_COMPRESS_INO() incorrectly treats the inode number as a meta inode, bypassing safety checks that validate inode ranges. This allows a corrupted directory entry pointing to an invalid inode number to be processed, potentially leading to system instability or security issues.

Detection Guidance

This vulnerability affects the Linux kernel's F2FS filesystem when the compress_cache mount option is disabled. Detection requires checking kernel logs for filesystem errors or examining mount options for F2FS partitions. Use commands like 'dmesg | grep F2FS' or 'mount | grep f2fs' to inspect filesystem behavior and mount options.

Impact Analysis

If exploited, this vulnerability could allow an attacker to cause a denial of service by triggering system crashes or corrupting filesystem data. It may also enable unauthorized access to sensitive data if the corrupted inode leads to unintended memory or disk access. Systems using the F2FS filesystem with the compress_cache option disabled are at risk.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards. It is a Linux kernel filesystem issue related to inode validation in the F2FS module, which could lead to filesystem corruption or crashes but does not involve data privacy or security controls typically governed by these regulations.

Mitigation Strategies

Apply the latest Linux kernel update to patch this issue. If using F2FS, ensure the compress_cache mount option is enabled only when needed. Monitor filesystem logs for suspicious inode errors or crashes.

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