CVE-2026-89702: Linux kernel nfsd fh_verify ring-buffer overflow

CVE-2026-89702 · Severity: critical · CVSS 9.8 · Published 2026-09-11

The Linux kernel's NFS server daemon (nfsd) contains a memory buffer overrun in its tracepoint logging code. When serving NFS requests over UDP, the kernel can write logging data beyond the allocated buffer size, potentially corrupting kernel memory. This could allow an attacker to crash the NFS server or execute arbitrary code with kernel privileges through malicious NFS requests.

Technologies: Linux Kernel. Vendors: Linux.

Quick answers

Is CVE-2026-89702 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-89702 being exploited in the wild.
How severe is CVE-2026-89702?
Critical severity, with a CVSS score of 9.8, published 11 September 2026.
Which products and versions are affected?
Linux Kernel affected versions unspecified in advisory.
Is there a fix for CVE-2026-89702?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-89702 attacked?
It is attacked over the network, in an operating system.
Am I affected by CVE-2026-89702?
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 exists in the nfsd_fh_verify and nfsd_fh_verify_err tracepoints, which declare a server sockaddr slot sized by xpt_remotelen but fill it with data from xpt_local using xpt_locallen. When xpt_locallen exceeds xpt_remotelen (which occurs on NFS/UDP where xpt_remotelen remains 0), the __assign_sockaddr memcpy writes past the reserved ring-buffer slot, causing a heap buffer overflow. The vulnerability is reachable on all NFSv2/v3-over-UDP requests, where 16 or 28 bytes are copied into a zero-byte slot. The fix sizes the server slot declaration with xpt_locallen to match the actual copy length, consistent with other NFSD tracepoints.

Affected products

  • Linux Linux kernel affected versions unspecified in advisory

Timeline

  • 2026-09-11: disclosed
  • 2026-09-11: advisory: CVE-2026-89702 published

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