# CVE-2026-89671: nfsd: gate nfs3 setacl by argp->mask

> An attacker can silently delete directory default ACLs via NFSv3 SETACL requests by omitting mask bits, bypassing intended access control modifications.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100827, BELL-CVE-2026-89671, DEBIAN-CVE-2026-89671, GHSA-j2pv-cprg-p57x, UBUNTU-CVE-2026-89671

## What is CVE-2026-89671?

CVE-2026-89671 is a critical missing authorization vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: gate nfs3 setacl by argp->mask

nfsd3_proc_setacl() calls set_posix_acl() unconditionally for both
ACL_TYPE_ACCESS and ACL_TYPE_DEFAULT, passing argp->acl_access and
argp->acl_default verbatim. The NFSv3 ACL decoder only populates
those pointers when the corresponding mask bit is set:

    nfs3svc_decode_setaclargs()
      if (args->mask & NFS_ACL)    decode into acl_access
      if (args->mask & NFS_DFACL)  decode into acl_default
      /* otherwise the pointer stays NULL (pc_argzero) */

    nfsd3_proc_setacl()
      set_posix_acl(.., ACL_TYPE_ACCESS,  argp->acl_access)
      set_posix_acl(.., ACL_TYPE_DEFAULT, argp->acl_default)

set_posix_acl(idmap, dentry, type, NULL) is the VFS "remove this
ACL type" operation. A NULL pointer that means "the client did not
send this arm" is therefore indistinguishable from "the client
asked to remove this ACL". A SETACL with mask=NFS_ACL silently
drops the directory's default ACL; mask=0 drops both.

The sibling nfsd3_proc_getacl() already consults argp->mask before
touching each arm; mirror that in setacl.

Fix by wrapping each set_posix_acl() call in the matching mask bit
check and initializing error to 0 before inode_lock so that a
request with neither bit set leaves the on-disk ACLs untouched and
returns nfs_ok. The out_drop_lock path and the unconditional
posix_acl_release() at out: are preserved; both NULL-tolerate the
skipped arms.

## Which versions are affected by CVE-2026-89671?


## How do I fix CVE-2026-89671?

Apply the vendor's patch.

## Is CVE-2026-89671 being exploited?

There is no known exploitation of CVE-2026-89671 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89671 and fix it if it is affected.

What it is: CVE-2026-89671 is a critical missing authorization vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89671 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89671/ (Markdown: https://insights.sbomify.com/CVE-2026-89671/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89671
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89671
- OSV: https://osv.dev/vulnerability/CVE-2026-89671

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89671/
Summaries are generated and may contain mistakes; the official description above is the record.