EUVD-2026-56136
GHSA-336f-j5cq-6c4f
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Unauthenticated network bypass grants a full interactive RDP session, implying both confidentiality and integrity impact to the vulnerable system.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3DescriptionCVE.org
FreeRDP before 3.30.0 contains a server-side authentication bypass in the RDSTLS handshake. When a server is configured with RdstlsSecurity = TRUE, the handshake dispatches inbound PDUs based solely on the attacker-supplied wire pduType without verifying that the received PDU is the one required at the current step. Because the rdpRdstls object is calloc-zeroed, its resultCode defaults to 0 (RDSTLS_RESULT_SUCCESS). An unauthenticated remote client can send a Capabilities PDU instead of the required Authentication Request PDU; rdstls_process_capabilities() returns success without ever setting resultCode, so the server responds with an AUTHRSP carrying resultCode SUCCESS and treats the session as authenticated without evaluating any password, redirection GUID, or auto-reconnect cookie. This affects the released FreeRDP 3.x series (e.g., 3.27.1) and master HEAD; at the time of the advisory no patched version was available.
AnalysisAI
Server-side authentication bypass in FreeRDP 3.x (confirmed through 3.27.1) allows an unauthenticated remote attacker to obtain a fully authenticated RDP session without supplying any credentials, GUID, or reconnect cookie when the server has RdstlsSecurity enabled. The flaw combines PDU-type confusion - the server routes inbound messages based solely on the client-supplied wire pduType without enforcing handshake state - with a calloc-zeroed result code that maps directly to RDSTLS_RESULT_SUCCESS, so sending a Capabilities PDU in place of the required Authentication Request PDU produces an unconditional authentication success response. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the FreeRDP server to be explicitly configured with RdstlsSecurity = TRUE to enable the RDSTLS security layer; this is not confirmed as the default server configuration, so stock deployments without explicit opt-in to RDSTLS are not exposed by this flaw. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 8.7 with vector AV:N/AC:L/AT:N/PR:N/UI:N accurately characterizes the attack - network-reachable, low complexity, unauthenticated, no interaction required - and VC:H confirms full confidentiality impact via unauthorized session access. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | The upstream fix is confirmed at commit b05a9510787c83c87ffc5fa8d7cc9f06ed971695 (https://github.com/FreeRDP/FreeRDP/commit/b05a9510787c83c87ffc5fa8d7cc9f06ed971695), which enforces RDSTLS handshake state machine correctness and changes the default resultCode to RDSTLS_RESULT_ACCESS_DENIED; however, a released tagged version (3.30.0) was not independently confirmed at advisory time, so operators should monitor the FreeRDP releases page and upgrade to the first release incorporating this commit once available. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all systems running FreeRDP 3.x (confirmed through version 3.27.1) with RdstlsSecurity enabled, prioritizing production RDP servers; if immediate patching is unfeasible, disable RdstlsSecurity as a temporary control. …
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FreeRDP is a free implementation of the Remote Desktop Protocol. Rated critical severity (CVSS 9.8), this vulnerability
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
Same weakness CWE-287 – Improper Authentication
View allSame technique Authentication Bypass
View allVendor StatusVendor
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External POC / Exploit Code
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