# CVE-2026-91958: FreeRDP 3.11.0 through 3.30.0 Heap Buffer Overflow via Monitor Index

> Attackers can trigger heap buffer overflows in FreeRDP by crafting malicious RDP files with invalid monitor indices, potentially leading to code execution or crashes.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-91958, GHSA-23pf-q83q-x45r, GHSA-qjqr-mv8g-x357, UBUNTU-CVE-2026-91958

## What is CVE-2026-91958?

CVE-2026-91958 is a medium-severity memory corruption vulnerability in Freerdp Freerdp, published on 15 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

FreeRDP versions before 3.31.0 fail to validate MonitorIds array values when parsing RDP connection files, allowing unbounded array indexing in xf_detect_monitors. Attackers can craft a malicious RDP file with an out-of-range selectedmonitors value to trigger out-of-bounds heap read and write operations when opened in xfreerdp.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-91958?

It affects 1 product.


Products: Freerdp Freerdp.

## How do I fix CVE-2026-91958?

Upgrade to a fixed version.

## Is CVE-2026-91958 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-91958 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-2026-91958 and fix it if it is affected.

What it is: CVE-2026-91958 is a medium-severity memory corruption vulnerability in Freerdp Freerdp, published on 15 Sep 2026. It can only be exploited from the same machine or local network, 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-2026-91958 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-2026-91958/ (Markdown: https://insights.sbomify.com/CVE-2026-91958/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91958
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91958
- OSV: https://osv.dev/vulnerability/CVE-2026-91958

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91958/
Summaries are generated and may contain mistakes; the official description above is the record.