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.DFU

DFU File

Device Firmware Upgrade File
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Verified by Adam B.· reviewed by FE Editorial ·updated Aug 22, 2026 3.3 (7 votes) Thanks for rating!
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A DFU file is a binary firmware image for a USB-connected hardware device, such as a microcontroller or USB peripheral. You flash it using dfu-util or STM32CubeProgrammer - you do not open it like a document. If you are trying to restore an iPhone or iPad, the firmware file Apple uses is .ipsw, not .dfu.

Developer: USB Implementers Forum (DFU suffix spec); device/firmware authors create device-specific content Category: System Files Open standard MIME: application/octet-stream
OPENS ON Windows macOS Linux
Related: .NOMEDIA · .DLL · .TMP · .LNK

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Last reviewed Aug 22, 2026

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What is the DFU file format?

.dfu files store firmware update data for USB-connected devices, following the USB Device Firmware Upgrade specification (USB-IF, revision 1.1, 2004). The format is primarily used for embedded systems and microcontrollers - STM32, Atmel, Nordic Semiconductor, and similar platforms - rather than consumer Apple devices, despite a common misconception.

Updating device firmware always carries a risk of damaging the device and should be performed with utmost care. Firmware is a software program embedded in the device's persistent memory in the form of a full operating system or an intermediate control layer. Firmware can be updated using .dfu files delivered over a USB connection. Damaged firmware can cause permanent damage to the device. Most modern devices employ security measures against update failure: the DFU suffix appends a CRC32 checksum to every .dfu file, allowing the device to verify integrity before applying the update.

A .dfu file consists of a device-specific firmware payload followed by a mandatory 16-byte DFU Suffix at the very end of the file. The suffix encodes the USB vendor ID, product ID, DFU specification version (bcdDFU), and the CRC32. STMicroelectronics extends the base format with a DfuSe variant used by STM32CubeProgrammer.

Apple's iOS DFU restore mode uses the same USB protocol, but Apple distributes firmware as signed .ipsw packages - not raw .dfu files.

Security & safety

RISK: MEDIUM

DFU files are firmware images intended to be flashed to hardware devices. Flashing incorrect or malicious firmware can brick a device permanently (bad firmware can corrupt bootloaders). Only flash .dfu files from the official device manufacturer. The file itself is inert as data; the risk is in executing the flash operation. Be cautious of websites distributing firmware - always verify against official manufacturer sources and check the CRC.

Format details

in a nutshell
FULL NAMEDevice Firmware Upgrade Fileaka DFU firmware file, USB DFU image
DEVELOPERUSB Implementers Forum (DFU suffix spec); device/firmware authors create device-specific contentsince 1999 (USB DFU specification 1.0 from USB-IF; revision 1.1 published 2004)
CATEGORYSystem Files
MIME TYPEapplication/octet-stream
TYPEBinary firmware image with USB DFU suffix (device-specific content + standard 16-byte tail)
STANDARDOpen · royalty-free
RELATED.nomedia.dll.tmp.lnk
This extension is also used by…
  • Apple iOS DFU mode - Apple devices support DFU mode (a USB device state) but Apple firmware is distributed as signed .ipsw files, not .dfu files; .dfu is not an Apple-specific extension.
MAGIC BYTES · FILE SIGNATURE
OFFSET
fffffffffffffff9fffffffffffffffafffffffffffffffb
HEX
444655
ASCII
DFU
The DFU signature is a SUFFIX, not a header. Last 16 bytes = DFU suffix: offset EOF-7: 55h ('U'), offset EOF-6: 46h ('F'), offset EOF-5: 44h ('D') - in reverse order, spells "DFU". Also includes: bcdDevice (2 bytes), idProduct (2 bytes), idVendor (2 bytes), bcdDFU (2 bytes, should be 0x011A), ucDfuSignature (3 bytes = DFU reversed), bLength (1 byte = 16), dwCRC (4 bytes CRC32 of file excluding dwCRC). The firmware payload before the suffix has NO standard magic bytes - format is device-specific (raw binary, Intel HEX stripped, ST DfuSe extension, etc.).

Programs that open DFU files

Windows2 apps
dfu-util Open-source Command-line: 'dfu-util -D firmware.dfu' to flash a DFU device; '-l' to list DFU devices. Download Windows binaries from project page.
STM32CubeProgrammer Free ST's GUI and CLI tool for flashing DFU/DfuSe firmware to STM32 devices. Supports .dfu (DfuSe format) and .bin/.hex.
macOS2 apps
dfu-util Open-source Install via Homebrew: 'brew install dfu-util', then 'dfu-util -D firmware.dfu'.
STM32CubeProgrammer Free Available for macOS; supports DfuSe .dfu files for STM32 devices.
Linux1 app
dfu-util Open-source Package in most distros ('apt install dfu-util', 'pacman -S dfu-util'). Use 'dfu-util -D firmware.dfu' to flash.

Technical details

deep spec
DFU suffix locationLast 16 bytes of the file - the DFU signature is a suffix, not a header
Suffix magicBytes at EOF-7 to EOF-5: `0x55`, `0x46`, `0x44` - spells `DFU` in reverse (`UFD`)
Integrity checkCRC32 over all file bytes except the final 4-byte `dwCRC` field itself; stored in the DFU suffix
Byte orderLittle-endian (DFU suffix fields as per USB-IF specification)
DFU spec version`bcdDFU` field in suffix: `0x0100` = DFU 1.0 (1999); `0x011A` = DFU 1.1 (2004)
Firmware payloadDevice-specific raw binary before the suffix - no standard magic bytes; format is vendor-defined
Vendor/product ID`idVendor` and `idProduct` fields in suffix identify the target USB device class
STMicroelectronics DfuSeExtended variant: `DfuSe` ASCII prefix at payload start; used by STM32CubeProgrammer for STM32 firmware
Apple distinctioniOS DFU restore uses the same USB protocol but firmware is distributed as signed `.ipsw` packages, not `.dfu` files
CompressionNone in the base DFU specification
Primary useEmbedded microcontrollers (STM32, Atmel/AVR, Nordic Semiconductor) and other USB-DFU-capable devices
Open specificationUSB DFU Specification Revision 1.1 (USB-IF, 2004) defines the suffix; firmware payload format is vendor-proprietary
Cross-platform tooling`dfu-util` open-source command-line tool supports standard DFU devices on Windows, macOS, and Linux
Released1999 (USB DFU specification 1.0 from USB-IF; revision 1.1 published 2004)
Latest versionUSB DFU Specification Revision 1.1 (2004, USB.org)
Open standardYes · royalty-free
Specificationwww.usb.org

DFU conversions

Possible
.DFU .BINGUIDE
Yes. The fastest way is dfu-util, which uploads firmware from a DFU device straight to a raw .bin file or…
How to convert
.DFU .HEXGUIDE
Yes, you can convert a DFU firmware file to Intel HEX with STM32CubeProgrammer's command-line converter in…
How to convert
Not possible
.DFU .IPSWWHY NOT?
No. A Device Firmware Upgrade File and an IPSW are firmware for completely different hardware. There is no…

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Frequently asked questions

How do I open a DFU file?
DFU files are not 'opened' like documents - they are flashed to hardware devices. Use dfu-util (command-line, free) or STM32CubeProgrammer (for STM32 devices) to write the firmware to the target device.
What is DFU mode on iPhone/iPad?
DFU mode on Apple devices is a USB device state that lets iTunes or Finder restore/update the device, but the firmware file is a .ipsw file, not a .dfu file. If you are restoring an iPhone, you don't need a .dfu file.
How do I know which DFU file is right for my device?
Download firmware only from your device manufacturer's official website. The DFU suffix contains the vendor ID and product ID (USB VID/PID) that must match your device; dfu-util will report an error if they don't match.
What is the difference between DFU and DfuSe?
DFU is the standard USB-IF specification. DfuSe is STMicroelectronics' proprietary extension for their STM32 devices, adding a 'DfuSe' prefix and memory mapping to the .dfu format. DfuSe files require STM32CubeProgrammer or compatible tools.
Can I convert a DFU file to BIN or HEX?
Yes - dfu-util can upload firmware from a DFU device to .bin, and STM32CubeProgrammer can convert between .dfu, .bin and .hex for STM32 devices. Stripping the 16-byte DFU suffix from a .dfu file yields the raw payload.

References

1USB DFU Specification Revision 1.1 (USB.org)www.usb.org
2dfu-util - Device Firmware Upgrade utilitydfu-util.sourceforge.net

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