CVE-2026-84270 in Red Hat
Summary
by MITRE • 09/01/2026
A flaw was found in the MTP backend in gvfs. When reading a file from a mounted MTP device, do_read() in gvfsbackendmtp.c trusts the data length returned by the device without limiting it to the original size requested by the client. If a malicious MTP device responds with more bytes than requested, this unrestricted length is passed directly to memcpy(). This causes the operation to read memory outside the intended boundaries. This allows an attacker who plugs in a malicious MTP device to cause a segmentation fault when a file is read and crash the gvfsd-mtp process, resulting in a denial of service.
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Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified within the GNOME Virtual File System backend for Media Transfer Protocol devices represents a critical failure in input validation during data retrieval operations. Specifically, the flaw resides in the do_read function located in the source file gvfsbackendmtp.c. This component is responsible for handling read requests from client applications that seek to access files stored on connected MTP-compliant hardware such as smartphones or digital cameras. The core technical deficiency lies in the assumption that the data length reported by the external device will never exceed the size originally requested by the local application. In secure software design, any input originating from an untrusted source, including peripheral devices, must be strictly validated against expected bounds before being processed further. Here, the backend blindly accepts the byte count provided by the MTP device without performing a comparative check against the initial request parameters.
This lack of boundary checking leads directly to a buffer over-read condition when the system attempts to copy data into memory. The unrestricted length value returned by the malicious or compromised MTP device is passed directly as an argument to the memcpy function, which copies bytes from the source location in the device's response buffer to a destination buffer allocated for the read operation. Because the copied size exceeds the intended limit, the memcpy call reads beyond the end of the valid memory region associated with that specific file transfer context. This action results in accessing memory addresses outside the designated boundaries, triggering undefined behavior within the application runtime environment.
The operational impact of this vulnerability is primarily a denial of service against the gvfsd-mtp daemon process. When an attacker connects a specially crafted MTP device to a victim's system and triggers a file read operation, the out-of-bounds memory access typically causes a segmentation fault. This crash terminates the gvfsd-mtp background service, which can disrupt file browsing capabilities for all users on the affected machine who rely on this backend for accessing media devices. While the primary manifestation is a crash leading to system instability and loss of functionality, such memory corruption issues often carry secondary risks including information disclosure if sensitive data from adjacent memory regions is inadvertently exposed during the read operation.
From a classification perspective, this vulnerability aligns with CWE-125 Out-of-bounds Read, which describes accessing memory beyond the intended boundaries of an array or buffer. It also relates to CWE-20 Improper Input Validation, as the system fails to verify that incoming data conforms to expected constraints before processing. In terms of attack vectors and tactics, this flaw is exploitable via ATT&CK technique T1564 Hide Execution Processes, where compromising a background service can disrupt user experience without necessarily gaining persistent access, though it serves as an entry point for further exploitation if the memory corruption allows for arbitrary code execution in more complex scenarios.
Mitigation strategies should focus on implementing strict input validation within the gvfs backend logic. Developers must ensure that any length value received from external devices is capped at the maximum size originally requested by the client application before being passed to memory copying functions like memcpy. Additionally, integrating static analysis tools and fuzzing tests targeting MTP protocol implementations can help identify similar boundary checking failures across other components of the virtual file system infrastructure. Users should be advised to exercise caution when connecting unknown or untrusted USB devices until patches are applied by distribution maintainers to update the gvfs package with these security fixes.