# CVE-2026-89703: Linux kernel nfsd use-after-free in delegation handling

Source: https://junglewise.ai/threats/cve-2026-89703-linux-kernel-nfsd-use-after-free-in-delegation-handling  
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-2026-89703 · Severity: critical · CVSS 9.8 · Published 2026-09-11

The Linux kernel's NFS server (nfsd) component failed to properly mark delegated file access permissions as freed when an administrator revoked them. This allows a use-after-free memory corruption bug to occur, where freed delegation objects are incorrectly re-added to a tracking list and later accessed during client cleanup, potentially allowing local attackers to crash the system or execute code with kernel privileges.

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

## Quick answers

**Is CVE-2026-89703 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-89703 being exploited in the wild.

**How severe is CVE-2026-89703?** Critical severity, with a CVSS score of 9.8, published 11 September 2026.

**Which products and versions are affected?** Linux Kernel Multiple kernel versions (affects delegation handling in nfsd).

**Is there a fix for CVE-2026-89703?** A patch was published on 2026-08-03: Upstream fix committed by Chuck Lever Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-89703 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-89703?** 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

A use-after-free vulnerability exists in the nfsd4_drop_revoked_stid() function in fs/nfsd/nfs4state.c. The function handles FREE_STATEID operations for admin-revoked delegations but fails to set the SC_STATUS_FREED flag before releasing the client lock (cl_lock). The revoke_delegation() function relies on this flag to detect whether FREE_STATEID has already processed a delegation; without it, the freed delegation object is incorrectly added to cl_revoked list via list_add(). This causes a use-after-free when cl_revoked is later traversed in __destroy_client() during NFS client cleanup. The fix sets SC_STATUS_FREED in the SC_STATUS_ADMIN_REVOKED path, matching the pattern already used in nfsd4_free_stateid(). Attack vector is local; no network exposure. Patch is available in upstream kernel.

## Affected products

- Linux Linux kernel Multiple kernel versions (affects delegation handling in nfsd)

## Timeline

- 2026-09-11: disclosed: CVE-2026-89703 published on NVD
- 2026-08-03: patched: Upstream fix committed by Chuck Lever
- 2026-09-07: patched: Fix included in stable kernel releases by Greg Kroah-Hartman

## References

- [https://git.kernel.org/stable/c/1e4795766719ffd74b8cf0f2fde4a1350f8326bf](https://git.kernel.org/stable/c/1e4795766719ffd74b8cf0f2fde4a1350f8326bf)
- [https://git.kernel.org/stable/c/650d370cfbc66a96dd14d517bd704689b5bda4e5](https://git.kernel.org/stable/c/650d370cfbc66a96dd14d517bd704689b5bda4e5)

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