# CVE-2026-80995: net: mctp: hold a reference to the route device in mctp_route_lookup()

> An unprivileged local user can trigger a use-after-free in the Linux kernel MCTP routing code, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-80995, GHSA-cvpj-275p-crg4, UBUNTU-CVE-2026-80995

## What is CVE-2026-80995?

CVE-2026-80995 is a high-severity use after free vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net: mctp: hold a reference to the route device in mctp_route_lookup()

mctp_route_lookup() uses rt->dev without holding a reference on it.
mctp_route_lookup_single() returns the route under RCU only, so the
route's device can be torn down concurrently: mctp_dev_put() drops the
last reference and synchronously kfree()s mdev->addrs.  mctp_dev_saddr()
then reads rt->dev->addrs[0], giving a use-after-free reachable by an
unprivileged local AF_MCTP user on the receive/forwarding path (no
CAP_NET_RAW required):

  BUG: KASAN: slab-use-after-free in mctp_route_lookup
  Read of size 1 at addr ... by task mctp_uaf/...
   mctp_route_lookup
   mctp_pkttype_receive
  Freed by task ...:
   kfree
   mctp_dev_put
   mctp_dev_notify

In the same window mctp_dst_from_route() -> mctp_dev_hold() also
increments a refcount that has already reached zero
("refcount_t: addition on 0 ... mctp_dev_hold").

This reintroduces the use-after-free class of CVE-2023-3439: the source
address lookup was moved ahead of the point where the destination takes
its device reference.

Take a reference with refcount_inc_not_zero() before touching rt->dev,
skip a device that is already dead, and drop the reference once the
destination has taken its own.

## Which versions are affected by CVE-2026-80995?


## How do I fix CVE-2026-80995?

Apply the vendor's patch.

## Is CVE-2026-80995 being exploited?

There is no known exploitation of CVE-2026-80995 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80995 and fix it if it is affected.

What it is: CVE-2026-80995 is a high-severity use after free vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80995 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-2026-80995/ (Markdown: https://insights.sbomify.com/CVE-2026-80995/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80995
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80995
- OSV: https://osv.dev/vulnerability/CVE-2026-80995

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80995/
Summaries are generated and may contain mistakes; the official description above is the record.