# CVE-2026-67303: FreeRDP before 3.29.0 Denial of Service via serial DeviceControl

> A reachable assertion in FreeRDP allows a malicious server to crash the client via a crafted serial device control request when redirection is enabled.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Aug 2026
- **Updated:** 3 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-67303, GHSA-4wq4-c34j-gg99, GHSA-pfxq-3qmw-8vjx, UBUNTU-CVE-2026-67303

## What is CVE-2026-67303?

CVE-2026-67303 is a medium-severity denial of service vulnerability in Freerdp Freerdp, published on 1 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

FreeRDP before 3.29.0 contains a reachable assertion (WINPR_ASSERT(OutputBufferLength == BytesReturned)) in serial_process_irp_device_control() in channels/serial/client/serial_main.c. When serial device redirection is enabled and a server-controlled IRP_MJ_DEVICE_CONTROL request specifies an unsupported IOCTL with a non-zero OutputBufferLength, CommDeviceIoControl() can fail with BytesReturned = 0, causing the mismatch to trigger the assertion and abort the client process (denial of service).

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-67303?

It affects 1 product.


Products: Freerdp Freerdp.

## How do I fix CVE-2026-67303?

Upgrade to a fixed version.

## Is CVE-2026-67303 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-67303 exists.

## Other vulnerabilities in Freerdp Freerdp

- [CVE-2021-37594](https://insights.sbomify.com/CVE-2021-37594/): Other in n/a (critical 9.8)
- [CVE-2021-37595](https://insights.sbomify.com/CVE-2021-37595/): Other in n/a (critical 9.8)
- [CVE-2026-67305](https://insights.sbomify.com/CVE-2026-67305/): FreeRDP Windows Client before 3.29.0 Heap Buffer Overflow via Cliprdr (critical 9.4)
- [CVE-2026-66402](https://insights.sbomify.com/CVE-2026-66402/): FreeRDP before 3.29.0 TLS Certificate Identity Validation Bypass (critical 9.3)
- [CVE-2026-67289](https://insights.sbomify.com/CVE-2026-67289/): FreeRDP before 3.29.0 HTTP Proxy Request Injection via Redirection (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67303 and fix it if it is affected.

What it is: CVE-2026-67303 is a medium-severity denial of service vulnerability in Freerdp Freerdp, published on 1 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-67303 exists.

Affected product: Freerdp Freerdp. 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-2026-67303/ (Markdown: https://insights.sbomify.com/CVE-2026-67303/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67303
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67303
- OSV: https://osv.dev/vulnerability/CVE-2026-67303

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67303/
Summaries are generated and may contain mistakes; the official description above is the record.