CVE-2026-111377 in FreeRDP
Summary
by MITRE • 10/16/2026
FreeRDP from 2.0.0 before 3.32.0 contains an unbounded reassembly vulnerability in WTSProcessChannelData that fails to enforce cumulative fragment limits. Authenticated clients can start a static virtual channel message, withhold the LAST flag, and send endless fragments to exhaust server memory.
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Analysis
by VulDB Data Team • 10/16/2026
The identified vulnerability resides within FreeRDP versions ranging from 2.0.0 up to but not including version 3.32.0, specifically affecting the WTSProcessChannelData function which handles data processing for terminal services channels. This component is responsible for managing virtual channel communications between the client and server in Remote Desktop Protocol environments. The core technical flaw is an unbounded reassembly issue where the implementation fails to enforce cumulative fragment limits during the reconstruction of multi-part messages. In standard protocol operations, incoming data streams are often segmented into smaller fragments that must be reassembled at the receiving end before processing can occur securely. However, in this specific code path, there is no mechanism to track or restrict the total size of these accumulated fragments over time.
An authenticated attacker can exploit this lack of boundary enforcement by initiating a static virtual channel message and deliberately withholding the LAST flag, which typically signals the final fragment of a sequence. By continuously sending additional data fragments without marking them as the end of the stream, the server is forced to keep allocating memory for each new piece of incoming data in an attempt to complete the reassembly process. Since there is no upper limit on how much memory can be consumed by this single logical connection or channel session, the server's available system memory will gradually deplete. This behavior constitutes a classic resource exhaustion scenario where legitimate services are starved of necessary resources due to malicious input patterns that exploit missing validation logic.
The operational impact of this vulnerability is primarily denial of service against the FreeRDP server instance. As memory consumption increases unchecked, the server may experience significant performance degradation, become unresponsive to other clients, or crash entirely when system limits are reached. This effectively disrupts availability for all users relying on the remote desktop infrastructure. From a threat modeling perspective, this flaw aligns with CWE-400, which describes conditions where resources are not properly limited before consumption, leading to resource exhaustion. Furthermore, in terms of adversary tactics and techniques, this exploitation vector corresponds to ATT&CK technique T1498.002, Network Denial of Service: Reflection Amplification, although the primary mechanism here is direct memory exhaustion rather than network bandwidth saturation, it falls under the broader category of resources being consumed through protocol abuse.
Mitigation strategies should focus on immediate patching and architectural hardening. The most effective remediation is to upgrade FreeRDP to version 3.32.0 or later, where this reassembly logic has been corrected to enforce strict cumulative fragment limits regardless of the presence of the LAST flag. For environments where upgrading is not immediately feasible, network-level controls such as rate limiting on virtual channel traffic and monitoring for unusually large or prolonged unfragmented sessions can help mitigate the risk. Additionally, implementing memory usage quotas per session at the application layer would provide an additional safeguard against runaway allocation requests. Security teams should also audit their remote desktop infrastructure to ensure that only authorized clients are permitted to establish static virtual channels, thereby reducing the attack surface available for such exploitation attempts.