CVE-2026-109248 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP 3.0.0 before 3.32.0 contains a heap out-of-bounds read in the WinPR clipboard function convert_filedescriptors_to_file_list(), which scans a server-controlled FILEDESCRIPTORW cFileName with unbounded _wcschr() and count_special_chars() calls without a NUL-termination guarantee. A malicious RDP server can send an odd-length FILEDESCRIPTORW blob in a CB_FORMAT_DATA_RESPONSE, crashing X11, Wayland, and SDL clients when the user pastes server-copied files.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified within FreeRDP versions prior to 3.32.0 represents a critical heap-based out-of-bounds read flaw located in the WinPR clipboard subsystem, specifically within the convert_filedescriptors_to_file_list() function. This component is responsible for processing file descriptor data received from remote desktop servers during clipboard operations involving files. The core technical deficiency stems from an inadequate validation of string termination when handling FILEDESCRIPTORW structures transmitted by a malicious RDP server. Specifically, the code relies on unbounded calls to _wcschr() and count_special_chars() to scan the cFileName field within these descriptors. These functions assume that the input buffer is properly NUL-terminated as per standard wide-character string conventions. However, when an attacker crafts a malformed CB_FORMAT_DATA_RESPONSE containing an odd-length FILEDESCRIPTORW blob, the assumption of valid termination fails. Because the length calculation does not account for potential misalignment or missing terminators in server-supplied data, the scanning functions continue reading memory beyond the allocated buffer boundaries until they encounter a NUL byte elsewhere in heap space.
This out-of-bounds read condition directly impacts the stability and integrity of client applications running on various graphical environments including X11, Wayland, and SDL-based interfaces. When an end-user initiates a paste operation for files copied from the malicious server, the application triggers the vulnerable code path. The subsequent memory access violation typically results in immediate process termination or crash, effectively causing a denial of service against the client system. While primarily observed as a stability issue leading to crashes, out-of-bounds reads can theoretically be leveraged for information disclosure if an attacker can carefully control heap layout and monitor side-channel effects, although the primary reported impact remains application instability. The vulnerability highlights significant gaps in input validation within remote desktop protocol implementations regarding how clipboard data is parsed and sanitized before processing.
From a classification perspective, this flaw aligns with CWE-125, which denotes Out-of-bounds Read vulnerabilities where software reads past the end of a buffer or array. It also relates to CWE-20, Improper Input Validation, as the application fails to verify that incoming data conforms to expected structural constraints such as proper string termination and length consistency. In terms of adversary tactics, this vulnerability can be exploited via ATT&CK technique T1567.002, which covers Exfiltration over Web Services if used in conjunction with other techniques for data staging, though its immediate utility lies more closely with disruption capabilities akin to denial-of-service vectors found in remote service exploitation chains. The attack vector is network-based and requires user interaction, specifically the act of pasting content from a compromised or maliciously configured RDP server into the local client environment.
Mitigation strategies for this vulnerability involve prioritizing the immediate upgrade of FreeRDP installations to version 3.32.0 or later where these bounds checking mechanisms have been corrected. For environments unable to patch immediately, administrators should enforce strict network segmentation policies that restrict access to RDP servers from untrusted networks and disable clipboard file transfer features if they are not operationally required. Additionally, implementing deep packet inspection solutions capable of detecting anomalous CB_FORMAT_DATA_RESPONSE payloads may provide a layer of defense against exploitation attempts. Security teams must also ensure that all client endpoints running X11, Wayland, or SDL interfaces with FreeRDP components are updated to mitigate the risk of service disruption caused by crafted clipboard data from potentially hostile remote desktop sessions.