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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This CVE exploits attack patterns that Casky's 0matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.
CVE-2026-67298 is a heap buffer overflow vulnerability in FreeRDP's server-side RAIL (Remote Application Integrated Locality) channel handler affecting versions 3.28.0 and earlier. The flaw stems from an integer underflow in the rail_server_handle_messages() function where the code subtracts RAIL_PDU_HEADER_LENGTH from a peer-controlled orderLength field without validating that orderLength meets the minimum header requirement. When orderLength values fall between 0-3, this subtraction causes an unsigned integer underflow, wrapping to an extremely large value and bypassing capacity checks (Stream_EnsureRemainingCapa). This allows attackers to write beyond allocated heap bounds, potentially achieving remote code execution on systems running vulnerable FreeRDP servers. The vulnerability has a CVSS score of 7.5 (high severity) and affects any organization deploying FreeRDP 3.28.0 or earlier in server configurations that expose the RAIL channel to untrusted network input.
While CVE-2026-67298 currently maps to CWE-191 (Integer Underflow) with no direct MITRE ATT&CK technique mapping, practitioners using Casky.ai would benefit from reconnaissance-focused security skills to identify FreeRDP server deployments and process memory analysis capabilities. Although Casky currently shows 0 matching skills for this specific CVE, defenders should prioritize detection of anomalous RAIL PDU processing patterns and heap memory corruption indicators. Security teams should focus on network segmentation to restrict RAIL channel exposure, implement strict input validation monitoring for orderLength field anomalies, and maintain current patching schedules. Extended reasoning capabilities through Claude AI would help analysts correlate this vulnerability with exploitation patterns like Execution (T1059) if code execution is achieved, and Persistence (T1547) if privilege escalation follows successful exploitation.
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