CVE-2026-91957 in FreeRDP
Summary
by MITRE • 09/15/2026
FreeRDP before 3.31.0 contains a use-after-free vulnerability in the smartcard RDPDR device handler when worker thread creation fails after device registration. Attackers can trigger thread creation failure during channel setup to cause device pointer deallocation while devman retains a reference, leading to crash or code execution.
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Analysis
by VulDB Data Team • 09/15/2026
The FreeRDP project is an open-source implementation of the Remote Desktop Protocol that enables cross-platform remote desktop connectivity. In versions prior to 3.31.0, a critical memory management flaw exists within the smartcard RDPDR device handler subsystem. This vulnerability stems from improper synchronization and reference counting logic during the initialization phase of virtual channel devices. Specifically, when the system attempts to register a new device via the Remote Desktop Protocol Device Redirection service, it spawns a dedicated worker thread to handle subsequent communication with that hardware component. The flaw manifests if this thread creation process fails due to resource exhaustion or other operational errors immediately after the device structure has been registered but before full initialization is complete.
Under normal operation, the device manager retains references to active devices to ensure they remain in memory while being accessed by various protocol handlers. However, when worker thread creation fails, the error handling routine incorrectly proceeds to deallocate the associated device pointer prematurely. This action occurs while the device manager still holds an active reference to that same memory location, assuming the device is fully operational and safe for future access. Consequently, a use-after-free condition arises where subsequent operations attempt to dereference or interact with the freed memory block through the stale pointer retained by the device management layer.
This architectural inconsistency allows attackers who can influence channel setup procedures to trigger this race-like state reliably. By forcing thread creation failures during the registration of smartcard redirection devices, an attacker can manipulate the lifecycle of these objects in memory. The immediate operational impact is a denial of service, as the application will likely crash due to accessing invalid memory addresses when it attempts to use the dangling pointer for standard device operations such as reading status or processing data packets.
Beyond simple crashes, this vulnerability poses severe risks regarding arbitrary code execution. If an attacker can control the contents of the freed memory region through heap spraying techniques or by manipulating adjacent allocations, they may achieve remote code execution within the context of the FreeRDP process. This is particularly dangerous in enterprise environments where FreeRDP clients connect to sensitive infrastructure, as it could allow lateral movement from a compromised client machine to internal network resources if combined with other exploitation vectors.
From a classification perspective, this issue aligns closely with CWE-416, which describes use-after-free errors resulting from improper memory management practices. The attack vector typically involves interacting with the RDP channel interface, potentially mapping to ATT&CK technique T1059, specifically command and script interpreters if code execution is achieved, or T1203 for exploitation of client software vulnerabilities. Mitigation strategies primarily involve upgrading FreeRDP to version 3.31.0 or later where the reference counting logic has been corrected to prevent premature deallocation during error paths. Additionally, administrators should enforce strict input validation on channel registration requests and limit exposure of RDP services to untrusted networks until patches are applied.