CVE-2026-67298 in FreeRDP
Summary
by MITRE • 08/01/2026
FreeRDP versions 3.28.0 and earlier contain a heap buffer overflow in the server-side RAIL channel handler (rail_server_handle_messages() in channels/rail/server/rail_main.c). When processing a RAIL PDU header, the code subtracts RAIL_PDU_HEADER_LENGTH from the peer-controlled orderLength field without first verifying orderLength is at least the header length. For orderLength values 0..3 this causes an unsigned integer underflow to a very large size, which bypasses the Stream_EnsureRemainingCapacity() capacity check (due to pointer arithmetic wraparound) and is then passed to WTSVirtualChannelRead(), resulting in an out-of-bounds heap write. A malicious or compromised RDP client can exploit this to corrupt the heap and crash the server. Fixed in FreeRDP 3.29.0.
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Analysis
by VulDB Data Team • 08/01/2026
The vulnerability under examination represents a critical heap buffer overflow flaw in FreeRDP server implementations affecting versions 3.28.0 and earlier, specifically within the server-side RAIL channel handler component. This issue manifests in the rail_server_handle_messages() function located in channels/rail/server/rail_main.c, where improper input validation leads to severe memory corruption consequences. The vulnerability stems from a fundamental flaw in how the system processes Remote Applications Integrated Architecture protocol data units, creating an exploitable condition that can be leveraged by malicious actors.
The technical execution of this vulnerability begins with the processing of RAIL PDU headers where the code performs a direct subtraction operation between orderLength field and RAIL_PDU_HEADER_LENGTH without prior validation. This arithmetic operation creates an unsigned integer underflow when the peer-controlled orderLength field contains values between 0 and 3, resulting in extremely large unsigned integer values that bypass subsequent security checks. The underlying mechanism involves pointer arithmetic wraparound that allows the system to pass these invalid buffer sizes to WTSVirtualChannelRead() function, which then executes out-of-bounds heap write operations. This particular implementation flaw directly violates established security principles for input validation and buffer boundary checking.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential remote code execution capabilities through heap corruption. An attacker controlling a compromised or malicious RDP client can exploit this condition to manipulate memory layout, potentially leading to arbitrary code execution on the vulnerable FreeRDP server. The nature of heap corruption means that the attack surface includes not only immediate system crashes but also the possibility of more sophisticated exploitation techniques that could escalate privileges or establish persistent access. This vulnerability represents a significant risk to enterprise environments where RDP services are exposed to untrusted networks or external clients.
Security mitigations for this vulnerability involve immediate deployment of FreeRDP version 3.29.0 which contains the necessary patches to prevent the integer underflow condition. Organizations should also implement network segmentation and access controls to limit exposure of RDP services to trusted networks only, while monitoring for potential exploitation attempts through log analysis of RAIL channel traffic patterns. The vulnerability aligns with CWE-129, specifically addressing improper validation of buffer size inputs, and corresponds to ATT&CK technique T1071.004 for application layer protocol manipulation. Additional defensive measures include implementing network-based intrusion detection systems that can identify anomalous RDP traffic patterns and configuring proper input sanitization at multiple layers of the network stack.
This vulnerability demonstrates the critical importance of robust input validation in server-side applications, particularly when handling peer-controlled data from potentially malicious sources. The flaw exemplifies how seemingly minor arithmetic operations can create devastating security implications when proper boundary checks are omitted. Organizations should conduct comprehensive vulnerability assessments of their RDP implementations and ensure all FreeRDP components are updated to versions that address this specific heap overflow condition. Regular security auditing of network protocols and channel handlers remains essential for identifying similar issues that could compromise system integrity and availability.