# CVE-2026-89713

## Summary

- **CVE ID:** CVE-2026-89713
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## Description

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

NFSD: check truncate permission under inode lock

nfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC
before it takes inode_lock(). The comparison uses the file size sampled
by that unlocked read, but the actual ATTR_SIZE update is applied later
under inode_lock() by notify_change().

This leaves a TOCTOU window for append-only files. If a client sends a
SETATTR that does not shrink the file at the time of the unlocked
sample, a concurrent append can extend the file before nfsd_setattr()
takes inode_lock(). notify_change() then applies a real truncation
without the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS
truncate syscall paths perform their own append-only checks before
calling notify_change(), so NFSD must make this decision against the
locked size it is about to change.

Split the write-count acquisition from the truncation permission check.
Keep get_write_access() before the locked setattr work, then recheck
whether the requested size is below i_size_read(inode) after inode_lock()
has been acquired and before notify_change(ATTR_SIZE). This also avoids
the plain unlocked inode->i_size load.

## Affected Products

- Linux — Linux (783112f7401ff449d979530209b3f6c2594fdb4e)
- Linux — Linux (604a3c407026d6162d15300478e63f901e435efc)
- Linux — Linux (cc4d5dc73841b98d33cdfb9822d70b0aac4beca5)
- Linux — Linux (3ee4f442e5b37a537297b812557b1163f96b5399)
- Linux — Linux (a3c6cbc4eac4473ed5461d5faae2794d3e5c0e44)
- Linux — Linux (982898d7f97a35447403c3fcecc0d96c646ce101)
- Linux — Linux (3.2.89)
- Linux — Linux (3.16.44)
- Linux — Linux (4.4.53)
- Linux — Linux (4.9.14)
- Linux — Linux (4.10.2)
- Linux — Linux (4.11)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/3afa17d93ba8c925f49370c816c6dae5112d8c24)
- [CNA](https://git.kernel.org/stable/c/d8352da196349182e1afd5a93308256cddc0a97d)
- [CNA](https://git.kernel.org/stable/c/44086254479035de42ca3d286ecf25521d4e6325)
- [CNA](https://git.kernel.org/stable/c/b778e0e0a16759f22a70579c3cf8d254a40d4a7f)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.60%
- **EPSS Percentile:** 47.3

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