# CVE-2025-39946: tls: make sure to abort the stream if headers are bogus

> A flaw in the Linux kernel TLS implementation allows remote attackers to cause a denial of service via crafted network packets that trigger an integer overflow in socket buffer handling.

- **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:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Oct 2025
- **Updated:** 5 Aug 2026
- **Also known as:** A-432728472, A-446648770, ASB-A-432728472, ASB-A-446648770, AZL-68141, BELL-CVE-2025-39946, DEBIAN-CVE-2025-39946, GHSA-cgf5-f6fj-4v5q, ROOT-OS-DEBIAN-12-CVE-2025-39946, ROOT-OS-DEBIAN-13-CVE-2025-39946, ROOT-OS-UBUNTU-2404-CVE-2025-39946, UBUNTU-CVE-2025-39946

## What is CVE-2025-39946?

CVE-2025-39946 is a critical vulnerability in Linux kernel, published on 4 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:

tls: make sure to abort the stream if headers are bogus

Normally we wait for the socket to buffer up the whole record
before we service it. If the socket has a tiny buffer, however,
we read out the data sooner, to prevent connection stalls.
Make sure that we abort the connection when we find out late
that the record is actually invalid. Retrying the parsing is
fine in itself but since we copy some more data each time
before we parse we can overflow the allocated skb space.

Constructing a scenario in which we're under pressure without
enough data in the socket to parse the length upfront is quite
hard. syzbot figured out a way to do this by serving us the header
in small OOB sends, and then filling in the recvbuf with a large
normal send.

Make sure that tls_rx_msg_size() aborts strp, if we reach
an invalid record there's really no way to recover.

## Which versions are affected by CVE-2025-39946?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39946?

Apply the vendor's patch.

## Is CVE-2025-39946 being exploited?

There is no known exploitation of CVE-2025-39946 in the wild and no public exploit code.

Public exploit code:

- Exploit for CVE-2025-39946, a bug in the Linux kernel's net/tls subsystem. (github_poc): https://github.com/farazsth98/exploit-CVE-2025-39946

## 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-2025-39946 and fix it if it is affected.

What it is: CVE-2025-39946 is a critical vulnerability in Linux kernel, published on 4 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-2025-39946 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-2025-39946/ (Markdown: https://insights.sbomify.com/CVE-2025-39946/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39946
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39946
- OSV: https://osv.dev/vulnerability/CVE-2025-39946

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39946/
Summaries are generated and may contain mistakes; the official description above is the record.