Linux Kernel up to 7.2.3 nfsd nfsd_direct_write cache containing sensitive information

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.3. It has been declared as very critical. Affected by this vulnerability is the function nfsd_direct_write of the component nfsd. The manipulation results in use of cache containing sensitive information. This vulnerability is identified as CVE-2026-89678. The attack can be executed remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2.3. Affected is the function nfsd_direct_write of the component nfsd. The manipulation with an unknown input leads to a use of cache containing sensitive information vulnerability. CWE is classifying the issue as CWE-524. The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix partial-write detection in nfsd_direct_write nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter); if (host_err < 0) return host_err; *cnt += host_err; if (host_err < segments[i].iter.count) break; /* partial write */ vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before write_iter: iter.count == original_len after write_iter: iter.count == original_len - host_err The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client. Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-89678 since 09/11/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/12/2026). The MITRE ATT&CK project declares the attack technique as T1592.

Upgrading to version 7.2.4 or 7.3-rc1 eliminates this vulnerability. Applying the patch fa6590dfd16ab55f03b658b079072ace3504825e/250ec14932d5cfe102f68a57892bb566eee7f83e is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3

License

• open-source

Website

• Vendor: https://www.kernel.org/

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