# CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions

> A flaw in Linux kernel TLS handling of zero-length records can cause a denial of service by breaking the receive message processing loop.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Yes, since 18 Sep 2026 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Sep 2025
- **Updated:** 7 Oct 2026
- **Also known as:** A-440544511, ASB-A-440544511, AZL-67001, BELL-CVE-2025-39682, DEBIAN-CVE-2025-39682, GHSA-v2pf-75pf-9c5h, ROOT-OS-DEBIAN-12-CVE-2025-39682, ROOT-OS-DEBIAN-13-CVE-2025-39682, ROOT-OS-UBUNTU-2404-CVE-2025-39682, UBUNTU-CVE-2025-39682

## What is CVE-2025-39682?

CVE-2025-39682 is a critical denial of service vulnerability in Debian Debian Linux, published on 5 Sep 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:

tls: fix handling of zero-length records on the rx_list

Each recvmsg() call must process either
 - only contiguous DATA records (any number of them)
 - one non-DATA record

If the next record has different type than what has already been
processed we break out of the main processing loop. If the record
has already been decrypted (which may be the case for TLS 1.3 where
we don't know type until decryption) we queue the pending record
to the rx_list. Next recvmsg() will pick it up from there.

Queuing the skb to rx_list after zero-copy decrypt is not possible,
since in that case we decrypted directly to the user space buffer,
and we don't have an skb to queue (darg.skb points to the ciphertext
skb for access to metadata like length).

Only data records are allowed zero-copy, and we break the processing
loop after each non-data record. So we should never zero-copy and
then find out that the record type has changed. The corner case
we missed is when the initial record comes from rx_list, and it's
zero length.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2025-39682?

It affects 3 products.


Products: Debian Debian Linux, Linux kernel, Siemens Simatic Cn 4100 Firmware.

## How do I fix CVE-2025-39682?

Apply the vendor's patch. US federal agencies must fix it by 21 Sep 2026.

## Is CVE-2025-39682 being exploited?

Yes. Attackers have exploited CVE-2025-39682 in the wild since at least 18 Sep 2026.

Public exploit code:

- A variant of CVE-2024-58239 (github_poc): https://github.com/khoatran107/cve-2025-39682
- Tracking CVE-2025-39682, the Linux kernel kTLS zero-length record use-after-free (github_poc): https://github.com/suominen/CVE-2025-39682

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)
- [CVE-2022-30333](https://insights.sbomify.com/CVE-2022-30333/): RARLAB UnRAR Directory Traversal (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39682 and fix it if it is affected.

What it is: CVE-2025-39682 is a critical denial of service vulnerability in Debian Debian Linux, published on 5 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2025-39682 in the wild since at least 18 Sep 2026.

Affected product: Debian Debian 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-2025-39682/ (Markdown: https://insights.sbomify.com/CVE-2025-39682/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39682
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39682
- OSV: https://osv.dev/vulnerability/CVE-2025-39682

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39682/
Summaries are generated and may contain mistakes; the official description above is the record.