# CVE-2026-91948: FreeRDP before 3.31.0 Out-of-bounds Write via SHOW_PROTOCOL

> Authenticated clients can trigger heap corruption in FreeRDP server-side channel handling, potentially leading to remote code execution.

- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Sep 2026
- **Updated:** 17 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-91948, GHSA-9jcm-x588-gh26, GHSA-vg28-cmpq-3hp8, UBUNTU-CVE-2026-91948

## What is CVE-2026-91948?

CVE-2026-91948 is a high-severity memory corruption vulnerability in FreeRDP, published on 15 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

FreeRDP versions before 3.31.0 contain an out-of-bounds write vulnerability in server-side static virtual channel handling when CHANNEL_OPTION_SHOW_PROTOCOL is enabled. Authenticated clients can queue oversized channel messages that cause buffer underflow and corrupt heap memory including live pointers, potentially enabling code execution.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-91948?


## How do I fix CVE-2026-91948?

Upgrade to a fixed version.

## Is CVE-2026-91948 being exploited?

There is no known exploitation of CVE-2026-91948 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91948 and fix it if it is affected.

What it is: CVE-2026-91948 is a high-severity memory corruption vulnerability in FreeRDP, published on 15 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-91948 in the wild and no public exploit code.

Affected product: 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-2026-91948/ (Markdown: https://insights.sbomify.com/CVE-2026-91948/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91948
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91948
- OSV: https://osv.dev/vulnerability/CVE-2026-91948

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91948/
Summaries are generated and may contain mistakes; the official description above is the record.