# CVE-2026-40033: FreeRDP - Heap-buffer-overflow in gdi_CacheToSurface via rectangle validation bypass

> Remote attackers can trigger heap-buffer-overflow in FreeRDP via malicious RDP servers, potentially achieving remote code execution or crashing the client.

- **Severity:** High 8.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/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:** 26 May 2026
- **Updated:** 27 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-40033, GHSA-xmr8-h8p4-932m, UBUNTU-CVE-2026-40033

## What is CVE-2026-40033?

CVE-2026-40033 is a high-severity memory corruption vulnerability in Freerdp Freerdp, published on 26 May 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 3.26.0 contains a heap-buffer-overflow vulnerability in gdi_CacheToSurface that allows remote attackers to write out-of-bounds heap memory. The vulnerability occurs because rectangle validation clamps coordinates to UINT16_MAX but performs copy operations using unclamped cache entry dimensions, enabling malicious RDP servers to trigger large out-of-bounds writes and potentially achieve remote code execution or client crash.

Weakness: CWE-787 (Out-of-bounds Write), CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-40033?

It affects 1 product.


Products: Freerdp Freerdp.

## How do I fix CVE-2026-40033?

Upgrade to a fixed version.

## Is CVE-2026-40033 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40033 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-2026-40033 and fix it if it is affected.

What it is: CVE-2026-40033 is a high-severity memory corruption vulnerability in Freerdp Freerdp, published on 26 May 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-2026-40033 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-2026-40033/ (Markdown: https://insights.sbomify.com/CVE-2026-40033/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40033
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40033
- OSV: https://osv.dev/vulnerability/CVE-2026-40033

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40033/
Summaries are generated and may contain mistakes; the official description above is the record.