# CVE-2026-63980: net/handshake: Use spin_lock_bh for hn_lock

> A deadlock in the Linux kernel's network handshake module can cause a denial of service when a softirq interrupts a process holding a lock.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 19 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63980, DEBIAN-CVE-2026-63980, GHSA-pf6j-pgmp-5g96, UBUNTU-CVE-2026-63980

## What is CVE-2026-63980?

CVE-2026-63980 is a high-severity vulnerability in Linux, published on 19 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: Use spin_lock_bh for hn_lock

nvmet_tcp_state_change(), a socket callback that runs in BH context,
can reach handshake_req_cancel() via nvmet_tcp_schedule_release_queue()
and tls_handshake_cancel().  handshake_req_cancel() acquires
hn->hn_lock with plain spin_lock().  If a process-context thread on
the same CPU holds hn->hn_lock when a softirq invokes the cancel path,
the lock attempt deadlocks.  This is the only caller that invokes
tls_handshake_cancel() from BH context; every other consumer calls it
from process context.

Deferring the cancel to process context in the NVMe target is not
straightforward: nvmet_tcp_schedule_release_queue() must call
tls_handshake_cancel() atomically with its state transition to
DISCONNECTING.  If the cancel were deferred, the handshake completion
callback could fire in the window before the cancel runs, observe the
unexpected state, and return without dropping its kref on the queue.
Reworking that interlock is considerably more invasive than hardening
the handshake lock.  Convert all hn->hn_lock acquisitions from
spin_lock/spin_unlock to spin_lock_bh/spin_unlock_bh so the lock is
never taken with softirqs enabled.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-63980?


## How do I fix CVE-2026-63980?

Apply the vendor's patch.

## Is CVE-2026-63980 being exploited?

There is no known exploitation of CVE-2026-63980 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63980 and fix it if it is affected.

What it is: CVE-2026-63980 is a high-severity vulnerability in Linux, published on 19 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-2026-63980 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-2026-63980/ (Markdown: https://insights.sbomify.com/CVE-2026-63980/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63980
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63980
- OSV: https://osv.dev/vulnerability/CVE-2026-63980

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63980/
Summaries are generated and may contain mistakes; the official description above is the record.