CVE-2026-109255 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP 3.0.0 before 3.32.0 contains an integer truncation vulnerability in license_check_stream_length that allows a malicious RDP server to trigger a heap buffer overflow on 32-bit clients. Attackers can send a crafted SERVER_LICENSE_REQUEST with a large scopeCount that bypasses length checks, causing out-of-bounds writes leading to denial of service or remote code execution.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in FreeRDP versions prior to 3.32.0 represents a critical security flaw rooted in improper integer handling within the Remote Desktop Protocol implementation. Specifically, the issue resides in the license_check_stream_length function, which is responsible for validating the integrity and boundaries of incoming data streams during the licensing phase of an RDP session establishment. This component plays a pivotal role in ensuring that the client correctly interprets server-provided licenses without exceeding allocated memory buffers. The core technical deficiency involves integer truncation, where large numerical values are incorrectly reduced to fit into smaller data types or insufficiently validated against buffer limits before allocation and usage.
In this specific scenario, an attacker operating as a malicious RDP server can exploit this flaw by sending a crafted SERVER_LICENSE_REQUEST packet containing an excessively large scopeCount value. Because the validation logic fails to properly account for the full magnitude of this integer on 32-bit client architectures, the subsequent memory allocation and copy operations are miscalculated. The system proceeds with out-of-bounds writes, effectively overflowing the heap buffer allocated for processing the license data. This behavior is characteristic of CWE-190, which describes Integer Overflow or Wraparound vulnerabilities that lead to other weaknesses such as buffer overflows when arithmetic results exceed expected bounds without proper checks.
The operational impact of this vulnerability is severe due to its potential for remote code execution and denial of service. Since the heap buffer overflow occurs during a network-received transaction initiated by an external server, it allows for arbitrary memory manipulation if the attacker can control the content written beyond the buffer boundaries. On 32-bit systems, which are more susceptible to certain types of integer truncation due to their fixed word size limitations, this flaw provides a reliable vector for executing malicious code with the privileges of the RDP client process. Additionally, even without successful exploitation for code execution, the memory corruption can cause immediate application crashes, resulting in a denial of service condition that disrupts remote desktop connectivity and productivity.
This vulnerability aligns with MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution, as it involves tricking a user into connecting to a malicious server that then exploits the client software itself. The attack vector is classified as Network-based because it requires only network access to the RDP service and does not necessarily require local authentication or physical access prior to exploitation. Mitigation strategies primarily involve updating FreeRDP to version 3.32.0 or later, where this integer truncation issue has been addressed through improved input validation and stricter boundary checks in the license stream processing logic. Organizations relying on older versions should implement network-level restrictions to prevent untrusted servers from initiating RDP connections until patches are applied, thereby reducing the attack surface available for exploitation.