# CVE-2026-89712: Linux kernel NFSD use-after-free in ssc_expire_umount

Source: https://junglewise.ai/threats/cve-2026-89712-linux-kernel-nfsd-use-after-free-in-ssc-expire-umount  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-11. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-89712 · Severity: critical · CVSS 9.8 · Published 2026-09-11

The Linux kernel's NFS server (NFSD) contains a use-after-free vulnerability in the inter-server copy mount management code. When processing expired mount entries, the code temporarily releases a lock and continues iterating using a saved pointer that can be freed by concurrent operations, leading to memory corruption. An attacker with network access to an NFS server could trigger a kernel crash or potentially execute code.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux).

## Quick answers

**Is CVE-2026-89712 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-89712 being exploited in the wild.

**How severe is CVE-2026-89712?** Critical severity, with a CVSS score of 9.8, published 11 September 2026.

**Which products and versions are affected?** Linux Kernel Multiple versions (2.6.11 through 6.x series affected; patched in stable branches).

**Is there a fix for CVE-2026-89712?** A patch was published on 2026-08-03: Patch merged in kernel mainline (commit 036c1b182f4da65363e79ec0ac276edc6b7296e5) Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-89712 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2026-89712?** Check whether you run Linux Kernel at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a use-after-free in the nfsd4_ssc_expire_umount() function within the Linux kernel's NFS server implementation (fs/nfsd/nfs4state.c). The function walks a list of mount entries using list_for_each_entry_safe() to iterate while releasing the nfsd_ssc_lock during mntput() operations. While the current entry is protected by the nsui_busy flag, the saved next pointer (tmp) is not pinned and can be freed by concurrent nfsd4_ssc_cancel_dul() calls from other RPC threads during the lock-drop window, causing dereferencing of freed memory on the next iteration. The fix restarts the walk from the list head after each unlock window rather than relying on a saved next pointer. The vulnerability affects inter-server copy operations in NFS, which are network-accessible and require no authentication beyond normal NFS access controls. A patch is available in the Linux kernel stable trees.

## Affected products

- Linux Linux kernel Multiple versions (2.6.11 through 6.x series affected; patched in stable branches)

## Timeline

- 2026-09-11: disclosed: CVE-2026-89712 disclosed
- 2026-08-03: patched: Patch merged in kernel mainline (commit 036c1b182f4da65363e79ec0ac276edc6b7296e5)
- 2026-09-14: patched: Patch released in stable kernels via Greg Kroah-Hartman

## References

- [https://git.kernel.org/stable/c/036c1b182f4da65363e79ec0ac276edc6b7296e5](https://git.kernel.org/stable/c/036c1b182f4da65363e79ec0ac276edc6b7296e5)
- [https://git.kernel.org/stable/c/2b59029b8f24a99b5d844af2da3950d39d36eeea](https://git.kernel.org/stable/c/2b59029b8f24a99b5d844af2da3950d39d36eeea)

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