CVE-2026-67296 Overview
CVE-2026-67296 is a denial of service vulnerability in FreeRDP versions before 3.29.0. The flaw resides in the Remote Desktop Protocol Extended Input (RDPEI) server channel handler. The handler fails to validate the maximum PDU body length before allocating a stream buffer. A malicious RDP client can send a header-only RDPEI message that declares a large body length, forcing the server to allocate excessive memory. The vulnerability is remotely exploitable over the network without authentication or user interaction and impacts service availability. It is classified under [CWE-20] Improper Input Validation.
Critical Impact
An unauthenticated remote attacker can exhaust server memory and cause denial of service against any FreeRDP-based server exposing the RDPEI channel.
Affected Products
- FreeRDP versions prior to 3.29.0
- Applications and services embedding the FreeRDP server library with RDPEI channel support
- Downstream distributions packaging vulnerable FreeRDP builds
Discovery Timeline
- 2026-08-01 - CVE-2026-67296 published to NVD
- 2026-08-03 - Last updated in NVD database
Technical Details for CVE-2026-67296
Vulnerability Analysis
The vulnerability is a resource exhaustion denial of service in the RDPEI server channel handler. RDPEI is the Remote Desktop Protocol Extended Input virtual channel used to transmit multitouch input from client to server. The handler reads a PDU header that contains a declared body length field. Before this fix, the handler used the declared length directly to allocate a receive stream without checking it against a maximum permitted PDU size. An attacker who controls or masquerades as an RDP client can transmit only the header, declare a very large body, and cause the server process to reserve large blocks of memory. Repeated messages amplify memory pressure and lead to service disruption or termination. The fix introduced in FreeRDP 3.29.0 adds an upper-bound check on the declared body length before stream allocation.
Root Cause
The root cause is missing input validation on an attacker-controlled length field, tracked as [CWE-20]. The RDPEI parser trusted the client-declared body length and used it as an allocation size parameter with no ceiling. No sanity check verified the value against a protocol-defined maximum or available system resources.
Attack Vector
Exploitation requires network access to a FreeRDP server that exposes the RDPEI virtual channel. Authentication is not required at the vulnerable code path when the channel handshake is reachable. The attacker sends a crafted RDPEI PDU consisting of a header with an inflated body length field and no accompanying body payload. See the FreeRDP GitHub Security Advisory and the VulnCheck Advisory on FreeRDP for protocol-level context.
No verified public exploit code is available at this time. The vulnerability mechanism is documented in prose in the upstream advisory.
Detection Methods for CVE-2026-67296
Indicators of Compromise
- Sudden growth in resident memory usage of FreeRDP server processes without a corresponding increase in active sessions
- RDP session terminations, out-of-memory kills, or service restarts on hosts running FreeRDP-based servers
- Inbound RDP connections from unexpected sources immediately preceding memory spikes or crashes
Detection Strategies
- Inspect RDPEI channel traffic for messages where the declared PDU body length is disproportionate to the actual bytes transmitted
- Alert on FreeRDP server process memory growth exceeding a baseline threshold within a short time window
- Correlate RDP connection logs with process crash and out-of-memory events on impacted hosts
Monitoring Recommendations
- Monitor version strings of deployed FreeRDP binaries and flag any instance below 3.29.0
- Track RDP connection rates and per-source connection counts to identify abusive clients
- Ingest host telemetry for OOM killer events and service restart loops on RDP-facing infrastructure
How to Mitigate CVE-2026-67296
Immediate Actions Required
- Upgrade FreeRDP to version 3.29.0 or later on all servers and embedding applications
- Restrict network exposure of RDP services to trusted networks or VPN-terminated segments
- Rebuild and redeploy any in-house software that statically links FreeRDP once the upgraded library is available
Patch Information
The fix is included in FreeRDP 3.29.0. The upstream project added validation of the maximum PDU body length before stream allocation in the RDPEI server channel handler. Refer to the FreeRDP GitHub Security Advisory GHSA-jm8r-22j6-4m4v for commit-level details and to distribution advisories for backported packages.
Workarounds
- Disable the RDPEI virtual channel on FreeRDP servers where multitouch input is not required
- Place FreeRDP servers behind a network gateway that enforces authenticated access before reaching the RDP listener
- Apply rate limiting and connection quotas on RDP-facing endpoints to reduce amplification impact
# Verify installed FreeRDP version and upgrade
xfreerdp --version
# Example upgrade on Debian/Ubuntu once patched packages are available
sudo apt update && sudo apt install --only-upgrade freerdp2-x11 freerdp3-x11
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
