# CVE-2026-63633: FreeRDP: Heap buffer overflow in Opus audio decode (`freerdp_dsp_decode_opus` resizes the wrong stream) — server→client

> A malicious RDP server can trigger a heap buffer overflow in FreeRDP clients using Opus audio, potentially leading to code execution or crashes.

- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:L/AT:P/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:** 19 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-63633, GHSA-72j9-356v-88xq, UBUNTU-CVE-2026-63633

## What is CVE-2026-63633?

CVE-2026-63633 is a high-severity memory corruption vulnerability in Freerdp Freerdp, published on 19 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 is a free implementation of the Remote Desktop Protocol. Prior to 3.28.0, freerdp_dsp_decode_opus in libfreerdp/codec/dsp.c calls Stream_EnsureRemainingCapacity on context->common.buffer even though opus_decode writes decoded PCM into the caller-supplied out stream. A malicious RDP server that negotiates WAVE_FORMAT_OPUS with a client built with WITH_OPUS enabled and WITH_DSP_FFMPEG disabled can make libopus write a large decoded frame beyond the 4096-byte StreamPool_Take destination used by channels/rdpsnd/client/rdpsnd_main.c. This can corrupt the client heap, crash the client, and may permit code execution. This issue is fixed in version 3.28.0.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-63633?

It affects 1 product.


Products: Freerdp Freerdp.

## How do I fix CVE-2026-63633?

Upgrade to a fixed version.

## Is CVE-2026-63633 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63633 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-2026-63633 and fix it if it is affected.

What it is: CVE-2026-63633 is a high-severity memory corruption vulnerability in Freerdp Freerdp, published on 19 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-2026-63633 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-2026-63633/ (Markdown: https://insights.sbomify.com/CVE-2026-63633/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63633
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63633
- OSV: https://osv.dev/vulnerability/CVE-2026-63633

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63633/
Summaries are generated and may contain mistakes; the official description above is the record.