# CVE-2025-68775: net/handshake: duplicate handshake cancellations leak socket

> Duplicate handshake cancellations in the Linux kernel cause a socket reference count underflow, leading to resource leaks and potential denial of service.

- **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:** 13 Jan 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-74456, BELL-CVE-2025-68775, DEBIAN-CVE-2025-68775, GHSA-jpgq-r68h-x9q2, ROOT-OS-UBUNTU-2404-CVE-2025-68775, UBUNTU-CVE-2025-68775

## What is CVE-2025-68775?

CVE-2025-68775 is a critical denial of service vulnerability in Linux, published on 13 Jan 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:

net/handshake: duplicate handshake cancellations leak socket

When a handshake request is cancelled it is removed from the
handshake_net->hn_requests list, but it is still present in the
handshake_rhashtbl until it is destroyed.

If a second cancellation request arrives for the same handshake request,
then remove_pending() will return false... and assuming
HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue
processing through the out_true label, where we put another reference on
the sock and a refcount underflow occurs.

This can happen for example if a handshake times out - particularly if
the SUNRPC client sends the AUTH_TLS probe to the server but doesn't
follow it up with the ClientHello due to a problem with tlshd.  When the
timeout is hit on the server, the server will send a FIN, which triggers
a cancellation request via xs_reset_transport().  When the timeout is
hit on the client, another cancellation request happens via
xs_tls_handshake_sync().

Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel
path so duplicate cancels can be detected.

Weakness: CWE-662 (Improper Synchronization)

## Which versions are affected by CVE-2025-68775?


## How do I fix CVE-2025-68775?

Apply the vendor's patch.

## Is CVE-2025-68775 being exploited?

There is no known exploitation of CVE-2025-68775 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68775 and fix it if it is affected.

What it is: CVE-2025-68775 is a critical denial of service vulnerability in Linux, published on 13 Jan 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-2025-68775 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-2025-68775/ (Markdown: https://insights.sbomify.com/CVE-2025-68775/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68775
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68775
- OSV: https://osv.dev/vulnerability/CVE-2025-68775

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68775/
Summaries are generated and may contain mistakes; the official description above is the record.