# CVE-2026-31611: ksmbd: require 3 sub-authorities before reading sub_auth[2]

> A missing bounds check in the Linux kernel ksmbd module allows out-of-bounds memory reads when parsing specific SIDs, potentially leaking data or causing crashes.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-83753, BELL-CVE-2026-31611, DEBIAN-CVE-2026-31611, GHSA-5q38-6rwh-6r7q, ROOT-OS-DEBIAN-12-CVE-2026-31611, ROOT-OS-UBUNTU-2204-CVE-2026-31611, ROOT-OS-UBUNTU-2404-CVE-2026-31611, UBUNTU-CVE-2026-31611

## What is CVE-2026-31611?

CVE-2026-31611 is a high-severity memory corruption vulnerability in Linux kernel, published on 24 Apr 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:

ksmbd: require 3 sub-authorities before reading sub_auth[2]

parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on
match reads sid.sub_auth[2] as the file mode.  If sid_unix_NFS_mode is
the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares
only min(num_subauth, 2) sub-authorities so a client SID with
num_subauth = 2 and sub_auth = {88, 3} will match.

If num_subauth = 2 and the ACE is placed at the very end of the security
descriptor, sub_auth[2] will be  4 bytes past end_of_acl.  The
out-of-band bytes will then be masked to the low 9 bits and applied as
the file's POSIX mode, probably not something that is good to have
happen.

Fix this up by forcing the SID to actually carry a third sub-authority
before reading it at all.

## Which versions are affected by CVE-2026-31611?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31611?

Apply the vendor's patch.

## Is CVE-2026-31611 being exploited?

There is no known exploitation of CVE-2026-31611 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31611 and fix it if it is affected.

What it is: CVE-2026-31611 is a high-severity memory corruption vulnerability in Linux kernel, published on 24 Apr 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-2026-31611 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31611/ (Markdown: https://insights.sbomify.com/CVE-2026-31611/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31611
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31611
- OSV: https://osv.dev/vulnerability/CVE-2026-31611

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31611/
Summaries are generated and may contain mistakes; the official description above is the record.