# CVE-2026-52947: net: qrtr: fix refcount saturation and potential UAF in qrtr_port_remove

> A race condition in the Linux kernel QRTR subsystem allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **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:** 24 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-90486, BELL-CVE-2026-52947, DEBIAN-CVE-2026-52947, GHSA-49c8-7mpf-m266, ROOT-OS-DEBIAN-11-CVE-2026-52947, ROOT-OS-DEBIAN-12-CVE-2026-52947, ROOT-OS-UBUNTU-2204-CVE-2026-52947, ROOT-OS-UBUNTU-2404-CVE-2026-52947, UBUNTU-CVE-2026-52947

## What is CVE-2026-52947?

CVE-2026-52947 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jun 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: qrtr: fix refcount saturation and potential UAF in qrtr_port_remove

In qrtr_port_remove(), the socket reference count is decremented via
__sock_put() before the port is removed from the qrtr_ports XArray and
before the RCU grace period elapses.

This breaks the fundamental RCU update paradigm. It exposes a race
window where a concurrent RCU reader (such as qrtr_reset_ports() or
qrtr_port_lookup()) can obtain a pointer to the socket from the XArray,
and attempt to call sock_hold() on a socket whose reference count has
already dropped to zero.

This exact race condition was hit during syzkaller fuzzing, leading to
the following refcount saturation warning and a potential Use-After-Free:

  refcount_t: saturated; leaking memory.
  WARNING: CPU: 3 PID: 1273 at lib/refcount.c:22 refcount_warn_saturate+0xae/0x1d0
  Modules linked in: qrtr(+) bochs drm_shmem_helper ...
  Call Trace:
   <TASK>
   qrtr_reset_ports net/qrtr/af_qrtr.c:768 [inline] [qrtr]
   __qrtr_bind.isra.0+0x48b/0x570 net/qrtr/af_qrtr.c:805 [qrtr]
   qrtr_bind+0x17d/0x210 net/qrtr/af_qrtr.c:901 [qrtr]
   kernel_bind+0xe4/0x120 net/socket.c:3592
   qrtr_ns_init+0x1a6/0x380 net/qrtr/ns.c:715 [qrtr]
   qrtr_proto_init+0x3b/0xff0 net/qrtr/af_qrtr.c:169 [qrtr]
   do_one_initcall+0xf5/0x5e0 init/main.c:1283
   ...
   </TASK>

Fix this by deferring the reference count decrement until after the
xa_erase() and the synchronize_rcu() complete.

(Note: The v1 of this patch incorrectly replaced __sock_put() with
sock_put(). As Simon Horman pointed out, the callers of qrtr_port_remove()
still hold a reference to the socket, so freeing the socket memory here
would lead to a subsequent UAF in the caller. Thus, the __sock_put() is
kept, but only repositioned to close the RCU race.)

Weakness: CWE-416 (Use After Free), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-52947?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52947?

Apply the vendor's patch.

## Is CVE-2026-52947 being exploited?

There is no known exploitation of CVE-2026-52947 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-52947 and fix it if it is affected.

What it is: CVE-2026-52947 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jun 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-2026-52947 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-52947/ (Markdown: https://insights.sbomify.com/CVE-2026-52947/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52947
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52947
- OSV: https://osv.dev/vulnerability/CVE-2026-52947

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52947/
Summaries are generated and may contain mistakes; the official description above is the record.