CVE-2026-111377 Overview
CVE-2026-111377 is a resource exhaustion vulnerability [CWE-400] in FreeRDP, an open-source implementation of the Remote Desktop Protocol (RDP). The flaw resides in WTSProcessChannelData, which fails to enforce cumulative fragment limits during static virtual channel reassembly. Authenticated clients can initiate a channel message, omit the LAST flag, and continuously send fragments until the server exhausts available memory. The vulnerability affects FreeRDP versions from 2.0.0 up to 3.32.0.
Critical Impact
Authenticated attackers can trigger server-side memory exhaustion, causing denial of service to FreeRDP-based remote desktop services.
Affected Products
- FreeRDP versions 2.0.0 through 3.31.x
- Applications and services linking against vulnerable FreeRDP libraries
- Server deployments exposing WTSProcessChannelData to authenticated RDP clients
Discovery Timeline
- 2026-10-16 - CVE-2026-111377 published to NVD
- 2026-10-20 - Last updated in NVD database
Technical Details for CVE-2026-111377
Vulnerability Analysis
FreeRDP implements static virtual channels to multiplex auxiliary data streams over an RDP session. Large messages are split into fragments, each tagged with flags such as CHANNEL_FLAG_FIRST and CHANNEL_FLAG_LAST. The server reassembles fragments into a single buffer before dispatching the message.
The function WTSProcessChannelData accepts fragments and appends them to a reassembly buffer tied to the active channel. It does not enforce an upper bound on the cumulative size of pending fragments. An authenticated client can start a message, continuously send fragment data, and never set the terminating LAST flag. The server allocates memory for each fragment until the host runs out of resources.
The issue is a classic uncontrolled resource consumption pattern. Because the attack requires only valid credentials and no user interaction, any user permitted to connect to the server can trigger it.
Root Cause
The root cause is missing enforcement of a maximum cumulative fragment size inside the channel reassembly path. The reassembly loop trusts client-supplied framing and will keep growing the backing buffer. The patch in FreeRDP 3.32.0 introduces cumulative limits that abort reassembly once a configured threshold is exceeded.
Attack Vector
Exploitation requires network access to an RDP service built on FreeRDP and valid session credentials. The attacker establishes an RDP session, opens a static virtual channel, and begins sending fragmented channel PDUs. Each fragment carries the FIRST flag or no flag, but never the LAST flag. The server allocates memory per fragment indefinitely, eventually degrading performance or crashing processes that depend on allocation success.
No verified exploit code is available in the enriched data. Refer to the VulnCheck Advisory for FreeRDP for additional technical context.
Detection Methods for CVE-2026-111377
Indicators of Compromise
- Sustained growth in resident memory of FreeRDP-based server processes without corresponding user activity.
- Authenticated RDP sessions that open static virtual channels and transmit fragmented PDUs over extended periods.
- Server crashes or OOM kills correlated with active RDP sessions from a single authenticated principal.
Detection Strategies
- Monitor process memory metrics for FreeRDP server binaries and alert on allocation rates that exceed historical baselines.
- Inspect RDP channel telemetry for sessions sending high volumes of fragments without CHANNEL_FLAG_LAST set.
- Correlate authentication logs with per-session resource consumption to identify abusive principals.
Monitoring Recommendations
- Enable verbose logging on FreeRDP server components and ship logs to a centralized analytics platform for anomaly review.
- Track per-user session counts and memory footprint to surface outliers that match the exhaustion pattern.
- Alert on repeated FreeRDP process restarts and link them to the originating session identifiers.
How to Mitigate CVE-2026-111377
Immediate Actions Required
- Upgrade FreeRDP to version 3.32.0 or later across all affected servers and dependent applications.
- Audit which services and products embed FreeRDP libraries and schedule coordinated updates.
- Restrict RDP access to trusted networks and enforce strong authentication for all accounts able to initiate sessions.
Patch Information
The FreeRDP maintainers released a fix in version 3.32.0 that enforces cumulative fragment limits inside WTSProcessChannelData. Review the GitHub Security Advisory GHSA-xm53-352c-57jw for patch details and backport guidance.
Workarounds
- Terminate long-running RDP sessions that have not completed channel reassembly within an operationally reasonable window.
- Apply per-session memory and connection quotas at the operating system or container level to cap blast radius.
- Limit which authenticated principals may open static virtual channels where the host application allows such granularity.
# Verify installed FreeRDP version and plan upgrade to 3.32.0 or later
xfreerdp --version
# Example: enforce a memory cap on the service via systemd
# /etc/systemd/system/freerdp-server.service.d/limits.conf
# [Service]
# MemoryMax=2G
# TasksMax=512
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
