# CVE-2026-64523: net/handshake: Take a long-lived file reference at submit

> A use-after-free vulnerability in the Linux kernel's handshake subsystem allows attackers to potentially execute code or escalate privileges.

- **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:** 25 Jul 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-93725, BELL-CVE-2026-64523, DEBIAN-CVE-2026-64523, GHSA-fc48-5g6g-x546, ROOT-OS-UBUNTU-2204-CVE-2026-64523, UBUNTU-CVE-2026-64523

## What is CVE-2026-64523?

CVE-2026-64523 is a critical use after free vulnerability in Linux, published on 25 Jul 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: Take a long-lived file reference at submit

handshake_nl_accept_doit() needs the file pointer backing
req->hr_sk->sk_socket to survive the window between
handshake_req_next() and the subsequent FD_PREPARE() and get_file().
The submit-side sock_hold() does not provide that.  sk_refcnt keeps
struct sock alive, but struct socket is owned by sock->file: when
the consumer fputs the last file reference, sock_release() tears
the socket down regardless of any sock_hold.

Add an hr_file pointer to struct handshake_req and acquire an
explicit reference on sock->file during handshake_req_submit().
handshake_complete() and handshake_req_cancel() release the
reference on the completion-bit-winning path.

The submit error path must also release the file reference, but
after rhashtable insertion a concurrent handshake_req_cancel() can
discover the request and race the error path.  Gate the error-path
cleanup -- sk_destruct restoration, fput, and request destruction
-- with test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED), the same
serialization handshake_complete() and handshake_req_cancel()
already use.  When cancel has already claimed ownership, the submit
error path returns without touching the request; socket teardown
handles final destruction.

The accept-side dereferences are not yet retargeted; that change
comes in the next patch.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-64523?


## How do I fix CVE-2026-64523?

Apply the vendor's patch.

## Is CVE-2026-64523 being exploited?

There is no known exploitation of CVE-2026-64523 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64523 and fix it if it is affected.

What it is: CVE-2026-64523 is a critical use after free vulnerability in Linux, published on 25 Jul 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-2026-64523 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-2026-64523/ (Markdown: https://insights.sbomify.com/CVE-2026-64523/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64523
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64523
- OSV: https://osv.dev/vulnerability/CVE-2026-64523

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64523/
Summaries are generated and may contain mistakes; the official description above is the record.