CVE-2023-53846: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53846 is a use-after-free vulnerability in the Linux kernel's F2FS (Flash-Friendly File System) subsystem, specifically in the truncate_dnode() function. The flaw was discovered via syzbot fuzzing on kernel version 6.4.0-rc7 and publicly disclosed on December 9, 2025. It affects the Linux kernel and was reported to Red Hat's security tracking system. The vulnerability carries a CVSS v3.1 base score of 5.5 (Medium), with a local attack vector and high availability impact (Red Hat Advisory, Red Hat Bugzilla).

The root cause is an out-of-bounds memory access (CWE-125/use-after-free, CWE-416) in truncate_dnode() within fs/f2fs/node.c. When inode A references inode B via inode B's inode number, and inode A is truncated, truncate_dnode() calls f2fs_truncate_data_blocks_range() to process data blocks in inode B's node page. The function traverses node->i.i_addr[0] through node->i.i_addr[ADDRS_PER_BLOCK() - 1] without validating that the referenced node page is a legitimate direct node, resulting in an out-of-boundary read of a freed slab object. The fix adds a sanity check on the dnode page in truncate_dnode(), introduces a new ERROR_INVALID_NODE_REFERENCE error recorded in the superblock for fsck detection, and removes the now-redundant f2fs_truncate_data_blocks() wrapper (Red Hat Bugzilla).

Successful exploitation causes a kernel KASAN (Kernel Address Sanitizer) slab-use-after-free read, which can crash the affected system, resulting in a denial of service (availability impact: High). There is no confidentiality or integrity impact identified, as the flaw is limited to an out-of-bounds read during file truncation operations on F2FS-formatted volumes. The scope is confined to the local system; lateral movement or remote exploitation is not applicable (Red Hat Advisory, Red Hat Bugzilla).

The fix is available as an upstream Linux kernel patch (commit references a6ec83786ab9 and af0f716ad3b0 in the stable tree). Users should update to a patched kernel version that includes the fix for fs/f2fs/node.c. Red Hat has tracked this via Bugzilla 2420324; users of Red Hat-based distributions should apply available kernel errata when released. SUSE has also issued advisories (SUSE-2026-0281-1 and SUSE-2026-20876-1) addressing this CVE. As a workaround, avoiding the use of F2FS filesystems on untrusted or user-accessible storage reduces exposure (Red Hat Bugzilla).