# CVE-2026-53181: vsock/vmci: fix sk_ack_backlog leak on failed handshake

> A resource leak in the Linux kernel's vsock/vmci module allows attackers to cause a permanent denial of service by exhausting the connection backlog.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 25 Jun 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-90627, BELL-CVE-2026-53181, DEBIAN-CVE-2026-53181, GHSA-6gq6-hxjh-9grq, ROOT-OS-DEBIAN-11-CVE-2026-53181, ROOT-OS-DEBIAN-12-CVE-2026-53181, ROOT-OS-UBUNTU-2204-CVE-2026-53181, ROOT-OS-UBUNTU-2404-CVE-2026-53181, UBUNTU-CVE-2026-53181

## What is CVE-2026-53181?

CVE-2026-53181 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 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:

vsock/vmci: fix sk_ack_backlog leak on failed handshake

When vmci_transport_recv_connecting_server() returns an error,
vmci_transport_recv_listen() calls vsock_remove_pending() but never
calls sk_acceptq_removed(). This leaves sk_ack_backlog incremented
permanently.

Repeated handshake failures (malformed packets, queue pair alloc
failure, event subscribe failure) cause sk_ack_backlog to climb
toward sk_max_ack_backlog. Once it reaches the limit the listener
permanently refuses all new connections with -ECONNREFUSED, a
silent denial of service requiring a process restart to recover.

The two existing sk_acceptq_removed() calls in af_vsock.c do not
cover this path: line 764 checks vsock_is_pending() which returns
false after vsock_remove_pending(), and line 1889 is only reached
on successful accept().

Fix by balancing sk_acceptq_added() with sk_acceptq_removed() on
the error path.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-53181?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53181?

Apply the vendor's patch.

## Is CVE-2026-53181 being exploited?

There is no known exploitation of CVE-2026-53181 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-2026-53181 and fix it if it is affected.

What it is: CVE-2026-53181 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 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-2026-53181 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-2026-53181/ (Markdown: https://insights.sbomify.com/CVE-2026-53181/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53181
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53181
- OSV: https://osv.dev/vulnerability/CVE-2026-53181

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53181/
Summaries are generated and may contain mistakes; the official description above is the record.