CVE-2026-25941 in FreeRDP
Summary
by MITRE • 02/25/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Versions on the 2.x branch prior to to 2.11.8 and on the 3.x branch prior to 3.23.0 have an out-of-bounds read vulnerability in the FreeRDP client's RDPGFX channel that allows a malicious RDP server to read uninitialized heap memory by sending a crafted WIRE_TO_SURFACE_2 PDU with a `bitmapDataLength` value larger than the actual data in the packet. This can lead to information disclosure or client crashes when a user connects to a malicious server. Versions 2.11.8 and 3.23.0 fix the issue.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2026-25941 affects FreeRDP implementations across multiple version branches, specifically targeting the RDPGFX channel functionality within the client component. This issue represents a critical out-of-bounds read condition that arises from insufficient input validation during packet processing. The flaw manifests when a malicious RDP server sends a specially crafted WIRE_TO_SURFACE_2 PDU message with an inflated `bitmapDataLength` field that exceeds the actual data payload. The vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions in software implementations. The RDPGFX channel serves as a graphics subsystem within the Remote Desktop Protocol that handles bitmap data transmission, making it a prime target for attackers seeking to exploit memory access violations.
The technical exploitation of this vulnerability occurs through a carefully constructed packet that manipulates the `bitmapDataLength` parameter to reference memory locations beyond the allocated buffer boundaries. When the FreeRDP client processes this malformed PDU, it attempts to read from uninitialized heap memory regions, potentially exposing sensitive data that may have been previously used by other application components. This memory disclosure can reveal information such as cryptographic keys, session tokens, or other confidential data stored in memory. The vulnerability is particularly concerning because it operates at the protocol level, allowing attackers to exploit the client-side implementation without requiring any special privileges or user interaction beyond establishing a legitimate RDP connection. The flaw demonstrates a classic buffer overflow pattern where the application fails to validate that the specified data length parameter corresponds to actual available data within the packet structure.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass potential denial-of-service conditions and escalation opportunities for more sophisticated attacks. When a user connects to a malicious RDP server, the client application becomes vulnerable to arbitrary memory reads that could expose sensitive information from the application's memory space. This type of vulnerability aligns with ATT&CK technique T1059.007, which covers execution through remote services, and can be leveraged as part of a broader attack chain to gather intelligence about the target system. The vulnerability affects both the 2.x and 3.x branches of FreeRDP, indicating that the underlying memory management flaw exists across multiple generations of the codebase, potentially increasing the attack surface. The specific nature of the vulnerability means that any user who connects to an unpatched FreeRDP client through a malicious RDP server could be compromised, making this a widespread concern for organizations relying on remote desktop connectivity.
Mitigation strategies for CVE-2026-25941 focus primarily on updating to the patched versions where the issue has been resolved through proper input validation and bounds checking. The fix implemented in FreeRDP versions 2.11.8 and 3.23.0 addresses the root cause by ensuring that the `bitmapDataLength` parameter is properly validated against the actual data length within the packet. Organizations should implement immediate patch management procedures to update all affected FreeRDP installations, particularly in environments where users connect to external or untrusted RDP servers. Network segmentation and firewall rules can provide additional protection by limiting direct access to RDP services from untrusted networks. Security monitoring should include detection of anomalous RDP packet structures, particularly those with suspiciously large `bitmapDataLength` values that could indicate exploitation attempts. The vulnerability also underscores the importance of proper memory management practices and input validation in protocol implementations, as similar issues could exist in other components of the RDP stack or related network services.