HIGH Introduced in 7.0
nfsd FileHandle UAF
CVE-2026-89687
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
KernelScan AI8.1HIGH
01Description
In the Linux kernel, the following vulnerability has been resolved: nfsd: ensure nfsd_file_do_acquire() does not use a non-opened file ->atomic_open is permitted to return success without actually opening the file. It indicates this by calling finish_no_open(). This means dentry_create() can return a file which hasn't been opened. This is extremely unlikely as ->atomic_open handlers typically use finish_no_open() only for already existing files, and dentry_create() isn't called in that case, and the parent being locked should prevent races. However out of an abundance of caution it seems wise to teach nfsd to only use the file returned by dentry_create() if FMODE_OPENED is set, indicating that it has in fact been opened.
02KernelScan AI Analysis
Risk summary
A remote attacker can exploit a vulnerability in the Linux kernel's NFS server (nfsd) to cause a denial of service or potentially execute arbitrary code. The vulnerability occurs when nfsd uses a file that has not been properly opened, which can lead to memory corruption.
Vulnerability analysis
The NFS server can use a file that was never actually opened. During file creation, the server requests a file from the underlying filesystem, which may report success without completing the open operation. The server previously checked only that it received a handle back, not that the open succeeded, so it could proceed with an invalid file object. This may lead to memory corruption or a system crash. The corrected code now confirms a file was truly opened before adopting it, otherwise falling back to open the file normally. A remote NFS client can reach this by requesting file creation on a filesystem that permits this incomplete open behavior.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| mainline | 7.0 | 7.3-rc1 | 5859cc01fee0 |
| 7.2 | 7.0 | 7.2.4 | a95a1cffacd0 |