CVE-2026-27015 in FreeRDP
Summary
by MITRE • 02/25/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.23.0, a missing bounds check in `smartcard_unpack_read_size_align()` (`libfreerdp/utils/smartcard_pack.c:1703`) allows a malicious RDP server to crash the FreeRDP client via a reachable `WINPR_ASSERT` → `abort()`. The crash occurs in upstream builds where `WITH_VERBOSE_WINPR_ASSERT=ON` (default in FreeRDP 3.22.0 / current WinPR CMake defaults). Smartcard redirection must be explicitly enabled by the user (e.g., `xfreerdp /smartcard`; `/smartcard-logon` implies `/smartcard`). Version 3.23.0 fixes the issue.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability CVE-2026-27015 affects FreeRDP, an open-source implementation of the Remote Desktop Protocol that enables remote desktop connections across various platforms. This security flaw exists in versions prior to 3.23.0 and represents a critical buffer overread condition that can lead to denial of service through client crash. The issue stems from inadequate input validation within the smartcard redirection functionality, specifically in the `smartcard_unpack_read_size_align()` function located in `libfreerdp/utils/smartcard_pack.c` at line 1703. The vulnerability manifests when a malicious RDP server sends specially crafted smartcard data that bypasses proper bounds checking mechanisms.
The technical exploitation of this vulnerability relies on a missing bounds check that should validate input data sizes before processing them. When a malicious RDP server sends oversized or malformed smartcard data, the function fails to verify that the data length falls within acceptable parameters. This oversight triggers a WINPR_ASSERT macro that ultimately leads to an abort() system call, causing the FreeRDP client to terminate abruptly. The crash condition is particularly concerning because it can be triggered remotely without requiring authentication, making it a significant threat vector for attackers who can establish RDP connections to vulnerable systems.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged for more sophisticated attacks within a broader exploitation framework. The issue affects systems where smartcard redirection is explicitly enabled through command-line parameters such as `/smartcard` or `/smartcard-logon` in xfreerdp connections. According to the ATT&CK framework, this vulnerability aligns with techniques involving privilege escalation and denial of service through client-side exploitation. The default configuration in FreeRDP 3.22.0 and earlier versions with `WITH_VERBOSE_WINPR_ASSERT=ON` means that many installations are potentially vulnerable without explicit configuration changes, creating a widespread attack surface.
Security implications of this vulnerability are compounded by the fact that smartcard redirection is often used in enterprise environments for authentication purposes, making it a valuable target for attackers seeking to disrupt critical infrastructure access. The vulnerability's classification under CWE-129 indicates a failure to perform proper input validation, specifically related to bounds checking in array access operations. Organizations using FreeRDP for remote desktop connections should prioritize immediate patching to version 3.23.0 or later, as the fix addresses the root cause by implementing proper bounds validation. Mitigation strategies include disabling smartcard redirection when not required, monitoring for unusual RDP connection patterns, and ensuring that all FreeRDP installations are updated to patched versions. The vulnerability demonstrates the importance of robust input validation in remote protocol implementations and highlights the need for comprehensive security testing of authentication and smartcard redirection components in remote desktop software.