# CVE-2025-40099: cifs: parse_dfs_referrals: prevent oob on malformed input

> A malicious SMB server can trigger an out-of-bounds memory access in the Linux kernel CIFS module via malformed DFS referral replies, potentially causing crashes or code execution.

- **Severity:** Critical 9.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 30 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-69436, BELL-CVE-2025-40099, DEBIAN-CVE-2025-40099, GHSA-58x9-22gw-84q7, ROOT-OS-DEBIAN-11-CVE-2025-40099, ROOT-OS-DEBIAN-13-CVE-2025-40099, ROOT-OS-UBUNTU-2204-CVE-2025-40099, ROOT-OS-UBUNTU-2404-CVE-2025-40099, UBUNTU-CVE-2025-40099

## What is CVE-2025-40099?

CVE-2025-40099 is a critical memory corruption vulnerability in Linux, published on 30 Oct 2025. 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:

cifs: parse_dfs_referrals: prevent oob on malformed input

Malicious SMB server can send invalid reply to FSCTL_DFS_GET_REFERRALS

- reply smaller than sizeof(struct get_dfs_referral_rsp)
- reply with number of referrals smaller than NumberOfReferrals in the
header

Processing of such replies will cause oob.

Return -EINVAL error on such replies to prevent oob-s.

## Which versions are affected by CVE-2025-40099?


## How do I fix CVE-2025-40099?

Apply the vendor's patch.

## Is CVE-2025-40099 being exploited?

There is no known exploitation of CVE-2025-40099 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40099 and fix it if it is affected.

What it is: CVE-2025-40099 is a critical memory corruption vulnerability in Linux, published on 30 Oct 2025. 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-2025-40099 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-2025-40099/ (Markdown: https://insights.sbomify.com/CVE-2025-40099/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40099
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40099
- OSV: https://osv.dev/vulnerability/CVE-2025-40099

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40099/
Summaries are generated and may contain mistakes; the official description above is the record.