CVE-2026-91962 in FreeRDP
Summary
by MITRE • 09/15/2026
FreeRDP before 3.31.0 contains an integer overflow in the audin Apple backends when processing FramesPerPacket values from MSG_SNDIN_OPEN messages. Attackers can supply crafted FramesPerPacket values that cause AudioQueueAllocateBuffer size computation to wrap, resulting in undersized buffer allocation and potential out-of-bounds access.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in FreeRDP versions prior to 3.31.0 represents a critical integer overflow flaw located within the audio input subsystem, specifically affecting the Apple backend implementation. This defect arises during the processing of MSG_SNDIN_OPEN messages, which are responsible for initializing and configuring the audio capture pipeline. The core technical issue stems from an inadequate validation mechanism when handling the FramesPerPacket parameter supplied by the client or server side of the Remote Desktop Protocol connection. In many audio APIs, including Apple's Audio Queue Services, buffer sizes are calculated based on packet counts multiplied by frame sizes to ensure sufficient memory allocation for real-time audio processing. When the FramesPerPacket value is crafted maliciously to be extremely large, it triggers an arithmetic overflow during this multiplication operation. Instead of allocating a sufficiently large contiguous block of memory, the system calculates a wrapped or truncated size that is significantly smaller than required.
This miscalculation leads directly to an undersized buffer allocation within the AudioQueueAllocateBuffer function call. Consequently, when subsequent audio frames are processed and written into this insufficiently sized buffer, the application performs out-of-bounds writes. This memory corruption allows for potential arbitrary code execution if an attacker can control the data being written or exploit specific heap layout conditions to overwrite critical pointers such as return addresses or function vtables. The impact is severe because it compromises the integrity of the host system running FreeRDP, potentially leading to full remote code execution with the privileges of the user process. This aligns closely with CWE-190, which defines integer overflow errors that can lead to other vulnerabilities like buffer overflows, and falls under the ATT&CK technique T1203, representing exploitation for client-side attacks where malicious input triggers unintended behavior in software applications.
From an operational perspective, this vulnerability highlights the risks associated with trusting external inputs even within established protocol implementations. FreeRDP is widely used to establish remote desktop sessions, meaning that connecting to a compromised or malicious RDP server could trigger this exploit without any user interaction beyond establishing the connection. The lack of rigorous bounds checking on numeric parameters like FramesPerPacket demonstrates a gap in defensive programming practices where input validation must be both syntactic and semantic, ensuring values fall within expected operational ranges before being used in arithmetic operations that affect memory management.
Mitigation strategies primarily involve upgrading to FreeRDP version 3.31.0 or later, where this integer overflow has been addressed through improved input validation and safer arithmetic handling. For environments unable to upgrade immediately, network-level controls such as firewalls can be configured to inspect RDP traffic for anomalous packet structures, although deep packet inspection of proprietary protocol fields remains challenging. Developers integrating FreeRDP should also ensure that their build configurations include stack protectors and address sanitizers during testing phases to detect similar issues early in the development lifecycle. Adhering to secure coding standards like CWE-134 regarding improper use of formatting specifiers or arithmetic operations can further reduce the risk of such memory corruption vulnerabilities arising from numeric input parameters.