CVE-2026-121960 in FreeRDP
Summary
by MITRE • 11/04/2026
FreeRDP before 3.32.2 contains a denial of service vulnerability in the NLA-enabled shadow server when a CredSSP TSRequest omits negoTokens. Unauthenticated attackers can send a crafted seven-byte TSRequest containing only the version field to trigger a fatal WINPR_ASSERT and abort the server process.
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Analysis
by VulDB Data Team • 11/04/2026
The identified security flaw resides within FreeRDP, specifically affecting versions prior to 3.32.2 when operating as an NLA-enabled shadow server. This vulnerability is classified under CWE-400, which denotes uncontrolled resource consumption leading to denial of service conditions. The root cause lies in the handling of CredSSP TSRequest messages during the authentication handshake process. Specifically, the software fails to adequately validate or handle cases where negoTokens are omitted from the incoming request structure. This lack of robust input validation allows an attacker to exploit a logic error that results in a fatal assertion failure within the WINPR library, which is integral to FreeRDP's processing pipeline.
From a technical perspective, the vulnerability is triggered by sending a specifically crafted network packet containing only seven bytes. This minimal payload consists solely of the version field within the TSRequest structure, deliberately omitting the negoTokens that are typically expected in a standard authentication flow. Because the server expects these tokens to proceed with secure negotiation, their absence causes an internal state mismatch. Instead of gracefully rejecting the malformed request or returning an appropriate error code, the application encounters an unexpected condition that triggers a WINPR_ASSERT macro. This assertion failure is not handled as a recoverable error but rather results in an immediate abort of the server process, effectively crashing the service.
The operational impact of this vulnerability is significant for any organization relying on FreeRDP's shadowing capabilities with Network Level Authentication enabled. An unauthenticated attacker can exploit this flaw remotely without needing valid credentials or prior access to the system. By simply sending the crafted seven-byte packet, the attacker can cause a denial of service by terminating the RDP server process. This disruption prevents legitimate users from connecting to remote desktops and may require manual intervention to restart the service, leading to downtime and potential loss of productivity. In environments where high availability is critical, such as data centers or enterprise IT support operations, this single-packet exploit can serve as a reliable method for disrupting services without requiring complex exploitation techniques.
This vulnerability aligns with MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under the sub-technique of service exhaustion through application crashes. The attack vector is classified as Network-based and Unauthenticated, allowing remote execution over standard RDP ports. To mitigate this risk, organizations must immediately update FreeRDP to version 3.32.2 or later, where the handling of incomplete TSRequest structures has been corrected to prevent assertion failures. Additionally, implementing network-level access controls such as firewalls that restrict RDP traffic to trusted IP ranges can provide a layer of defense in depth. Monitoring for unusual spikes in connection attempts or process restarts may also aid in detecting exploitation attempts before significant disruption occurs.