# CVE-2026-89711

## Summary

- **CVE ID:** CVE-2026-89711
- **Severity:** HIGH
- **CVSS Score:** 8.2 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check

The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in
fh_verify of directories") details the assumption that justified
adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is
invalid (in the case of NFS reexport).

When NFSD exports an NFS filesystem it is very possible for
nfsd_mode_check() to encounter a @dentry that doesn't have
i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and
NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()).

So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir
return on that branch must stay. It guards the subsequent
lookup_one_unlocked() -> __lookup_slow() path, which calls
inode->i_op->lookup() with no NULL check, so returning nfserr_notdir
is what keeps a client LOOKUP into such a @dentry from dereferencing
a NULL method pointer.

## Affected Products

- Linux — Linux (e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c)
- Linux — Linux (4.8)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/b55b4d880bb080fa10eb08ba21a5d8679b8102fe)
- [CNA](https://git.kernel.org/stable/c/7ef182a8fe9c12b0d936880b1e504840639aa009)
- [CNA](https://git.kernel.org/stable/c/a275de3bac5635514ca830f2e46b5ff0e66b5c4c)
- [CNA](https://git.kernel.org/stable/c/aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e)
- [CNA](https://git.kernel.org/stable/c/ae251937c6f0237e5b555a5e4ba4595b8206e865)
- [CNA](https://git.kernel.org/stable/c/e145e8d67a5d41c72d322e7f87ab474d39d9dfb7)
- [CNA](https://git.kernel.org/stable/c/9f4434893a2783f7384d993cea883aff3fb7a52d)
- [CNA](https://git.kernel.org/stable/c/2ef131323999539038e306773c8256403834361b)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.45%
- **EPSS Percentile:** 38.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._