FreeRDP shadow server: Missing authentication allows keystroke injection
Summary
The shadow server of FreeRDP, which shares a live desktop over RDP, processes input events before the client has authenticated. An unauthenticated network attacker who negotiates TLS-only RDP can inject synthetic keystrokes into the logged-in user's X11 session via XTEST. Exploitation requires a reachable shadow listener on a Linux/X11 host with interaction enabled, which is the default; the impact is limited to integrity (no data read is demonstrated).
Affected
- FreeRDP 3.0.0 up to but excluding 3.32.0 (CNA and NVD range)
- The GitHub advisory lists 3.0.0 to 3.31.1 as affected
- Only builds with the X11 shadow backend and XTEST are demonstrated to be exploitable
Fixed in
- FreeRDP 3.32.0 (released 23 Sep 2026)
- Linux distributions ship fixed builds under their own package versions; check your distribution's advisory
Workaround
- No vendor-documented workaround.
- Interim measures (recommendations, not vendor guidance): disable the shadow server if it is not needed, restrict the RDP port to known management networks, and do not expose it to the internet.
Exploitation
- Not listed as known exploited (CISA KEV: no).
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- No public proof of concept found in the research; the vendor advisory describes a lab reproduction.
Our recommendation
- Check whether freerdp-shadow servers are installed (for example freerdp3-shadow-x11) and whether they are reachable from untrusted networks.
- Update to FreeRDP 3.32.0 or the fixed distribution package.
- Disable the shadow server where it is not required.
- Restrict RDP access to management networks and monitor for unexpected keyboard input in active sessions.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-m998-cvfm-9444 github.com
- VulnCheck advisory www.vulncheck.com
- FreeRDP 3.32.0 release www.freerdp.com
- Ubuntu security tracker CVE-2026-110838 ubuntu.com
- OSV UBUNTU-CVE-2026-110838 osv.dev
- VulDB CVE-2026-110838 vuldb.com
- OpenCVE CVE-2026-110838 app.opencve.io
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 02:43.
Original description (NVD)
FreeRDP shadow server from 3.0.0 before 3.32.0 dispatches input PDUs during the Confirm Active state before authentication, allowing unauthenticated attackers to inject keyboard input. Attackers can negotiate TLS-only RDP and send an input PDU without Confirm Active to inject synthetic keystrokes into the host user's X11 session via XTEST.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.