CVE-2026-89787 is a vulnerability in Linux Kernel
Published on September 16, 2026
ext4: check dir entry fits before reading the hash trailer in ext4_search_dir()
In the Linux kernel, the following vulnerability has been resolved:
ext4: check dir entry fits before reading the hash trailer in ext4_search_dir()
For casefolded encrypted directories ext4 stores an 8-byte hash trailer
after the name (EXT4_DIRENT_HASHES()), at an offset derived from
de->name_len. On the sb_no_casefold_compat_fallback() path ext4_match()
reads that trailer, but ext4_search_dir()'s by-hand pre-check only tests
de->name + de->name_len <= dlimit, which proves the name fits, not the
rounded trailer. A crafted entry whose name ends at the block boundary
passes the check while EXT4_DIRENT_HASHES(de) lands past the block end,
so ext4_match() reads out of bounds on an ordinary lookup. KASAN reports
it as a use-after-free when the page after the directory block holds a
freed object:
BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435)
Read of size 4 at addr ffff888010458000 by task exploit
Call Trace:
ext4_match (fs/ext4/namei.c:1435)
ext4_search_dir (fs/ext4/namei.c:1470)
__ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632)
ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769)
...
filename_lookup (fs/namei.c:2842)
vfs_statx (fs/stat.c:353)
__do_sys_newfstatat (fs/stat.c:538)
do_syscall_64 (arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Require, for hash-in-dirent directories, that the whole entry including
the rounded trailer fits before calling ext4_match(). This is the same
bound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so
no well-formed entry is rejected. The other caller, ext4_find_dest_de(),
runs ext4_check_dir_entry() first and is unaffected.
Products Associated with CVE-2026-89787
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Affected Versions
Linux:- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below 4d20106c536b73c4a8a02652dc85e35898baebf7 is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below 61a395967de06edba58760e81907a272db749faa is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below e94676a08af6312aa72d8a981232b281f9bcfcf5 is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below d8c184bec24b5a00ae96d704856d935eaded1685 is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below 3933884bc3102898b458c53fbd1ac52eb9cdb8a4 is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below 83663c0b739480c00cfe785675db87520ec484ed is affected.
- Version 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 and below c7e6b863d298f56522d0d08554bbea7f142e6588 is affected.
- Version 5.13 is affected.
- Before 5.13 is unaffected.
- Version 5.15.221, <= 5.15.* is unaffected.
- Version 6.1.188, <= 6.1.* is unaffected.
- Version 6.6.157, <= 6.6.* is unaffected.
- Version 6.12.110, <= 6.12.* is unaffected.
- Version 6.18.52, <= 6.18.* is unaffected.
- Version 7.2.6, <= 7.2.* is unaffected.
- Version 7.3-rc1, <= * is unaffected.