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iPhone Errors

How to Fix iTunes Error 27 When Restoring iPhone

By ErrorFix · Updated October 26, 2026 · 8 min read

Error 27Plain English: iTunes or Finder was restoring your iPhone, hit a problem talking to the phone or to Apple's servers, and gave up with an unknown error message.
Quick answer: Error 27 means iTunes or Finder could not finish restoring your iPhone. Use an Apple-certified cable on a direct USB port, restart both devices, update iTunes or macOS, temporarily disable security software, turn off any proxy, delete the damaged firmware download, and try a different computer before concluding the phone itself is at fault. The full steps are below.

What error 27 means

Error 27 appears in iTunes on Windows or Finder on a Mac while you are restoring or updating an iPhone. The message reads, "The iPhone could not be restored. An unknown error occurred (27)," and the phone typically stays in recovery mode, showing the computer-and-cable screen and waiting for a restore that will actually complete. Your data is still on the phone at this point, and nothing is permanently broken — the attempt simply never finished.

The "unknown error" label hides a very ordinary meaning in most cases. A restore is a long, chatty conversation: the computer sends firmware in chunks, the iPhone acknowledges each one, and the computer also checks in with Apple's servers to verify that the firmware is signed for your device. Error 27 means that conversation broke down somewhere along the way — the computer sent data the phone never confirmed, a security tool or proxy blocked the server check, or the firmware file itself was damaged or mismatched. That makes it a connection-and-software failure first, and a hardware question second.

Error 27 does have a hardware side that its close neighbor, error 26, mostly lacks. On older iPhones, and on phones that have had third-party repairs, error 27 has been linked to firmware mismatches and to hardware faults that prevent the restore from completing. That is why the order of the fixes below matters: work through every free, computer-side fix first, and only treat the phone as faulty once a different computer and a DFU restore have both failed. Jumping straight to a repair shop skips fixes that cost nothing and solve the problem in many cases.

Common causes

How to fix error 27 — step by step

Work through these in order. Error 27 resolves at the cable, the restart, or the network setting in many cases — save the DFU restore for last, since it erases the phone.

  1. Swap the USB cable and port. Error 27 is often a broken link between the computer and the iPhone during a restore, and the cable is the weakest point in that link. Use an Apple-certified cable, plug it directly into the computer with no USB hub, dock, keyboard port, or extension cable in between, and on a desktop PC choose a rear USB port, which supplies steadier power than the front ones. If the cable only works when held at an angle, or the connector feels loose, replace it outright. Then start the restore again from the beginning.
  2. Restart the iPhone and the computer. A full restart clears a stuck USB session and any half-finished restore state on both devices. On Windows, choose Restart from the Start menu rather than Shut down, so Windows genuinely reloads its USB drivers instead of resuming a saved session. If the iPhone is sitting in recovery mode, hold the Side button and either Volume button until the screen changes, then put it back into recovery once the computer is back up. Run the restore with nothing else competing for the computer — close browsers, pause downloads, and stop any streaming.
  3. Update iTunes, the Apple Devices app, or macOS. Older restore software is a common trigger for error 27 because Apple changes the restore protocol and the firmware signing checks over time. In classic iTunes on Windows, click Help at the top of the window and choose Check for Updates. If you use the separate Apple Music and Apple Devices apps on Windows 10 or 11, update them from the Microsoft Store under Library. On a Mac, Finder handles restores, so keep macOS current through System Settings, General, Software Update. Restart the computer after updating, then retry the restore.
  4. Temporarily disable security software. Antivirus programs, firewalls, and endpoint-protection tools can interrupt the steady stream of data between iTunes and the iPhone, and that interruption surfaces as error 27. On Windows, open Windows Security, go to Virus and threat protection, and pause real-time protection for the duration of the restore; also confirm that iTunes or the Apple Devices app is allowed through the firewall. Run the restore while the protection is paused, then turn everything back on immediately afterward.
  5. Turn off any proxy and delete the downloaded firmware. During a restore, iTunes or Finder must reach Apple's servers to verify the firmware, and a proxy server or a filtered network can block that check and produce error 27. On Windows, open Settings, Network and internet, Proxy, and turn off Use a proxy server and Automatically detect settings if a manual proxy is configured. On a Mac, open System Settings, Network, and check the proxy settings for the active connection. If you are on a school, office, or public network, try a home network or a phone hotspot instead. A damaged firmware download can also make the restore fail at the same point every time. On Windows, open File Explorer and go to Users, your username, AppData, Roaming, Apple Computer, iTunes, iPhone Software Updates, and delete the .ipsw file there. On a Mac, open Finder, press Command, Shift, and G, type ~/Library/iTunes/iPhone Software Updates, and delete the .ipsw file. Then start the restore again so iTunes downloads a fresh, complete copy.
  6. Try another computer, or use DFU mode as a last resort. If the error persists on one machine, try the restore on a different computer — success there proves the iPhone is fine and the original computer was at fault. If no second computer helps, a Device Firmware Update restore is the last resort: it reloads the bootloader and the operating system from scratch. Connect the iPhone, then press and quickly release Volume Up, press and quickly release Volume Down, hold the Side button for 10 seconds, then — still holding Side — hold Volume Down for 5 seconds, release Side, and keep holding Volume Down for about 10 more seconds. The screen stays completely black in DFU mode. iTunes or Finder will detect a device in recovery and offer a restore; accept it. DFU mode erases the iPhone, so restore your data from an iCloud or computer backup afterward. If even a DFU restore fails with error 27, the cause is very likely hardware, and the phone needs professional service.

Did this fix it? Quick checklist

If error 27 survives a new cable, a restart, updated software, disabled security tools, a proxy-free network, a fresh firmware download, and a DFU restore on two different computers, you have ruled out every common cause and the problem is very likely the iPhone's hardware — a firmware mismatch from an earlier repair, or a failing component. Book an appointment at an Apple Store or authorized service provider — mentioning that you already tried DFU mode on two computers skips the first round of their diagnostics.

Frequently asked questions

What does iPhone error 27 mean?

Error 27 means iTunes or Finder could not complete a restore or update and aborted with the message 'The iPhone could not be restored. An unknown error occurred (27).' It is usually a failure in the connection between the computer and the iPhone, in the computer reaching Apple's servers during the restore, or in the firmware itself — and on older devices it can also point to a hardware fault.

Is error 27 a hardware problem with my iPhone?

It can be, more often than its neighbors like error 26. Error 27 has a known hardware side, especially on older iPhones and on phones with third-party parts. But you should still rule out the cable, the port, outdated restore software, security tools, a proxy server, and a damaged firmware download first, because those are free to fix and they account for many error 27 cases. If the restore succeeds on a different computer, your iPhone hardware is fine.

Why does error 27 keep happening at the same point in the restore?

A failure that repeats at the same progress point points to one consistent cause rather than a random glitch. If it fails while verifying or installing the software, suspect a damaged firmware download on the computer and delete the .ipsw file so iTunes fetches a fresh copy. If it fails right at the start, suspect the cable, the port, or a proxy or security tool blocking the connection instead.

How is error 27 different from errors 26 and 29?

Error 26 is almost always a computer-side connection or network failure and is very fixable at home. Error 27 sits one step closer to hardware: it shares the same cable, software, and network causes as error 26, but it is also linked to firmware mismatches and hardware faults, so it survives the easy fixes more often. Error 29 is different again — it is most often a battery problem. If you are seeing 27 rather than 29, do not replace the battery first; work through the cable, software, network, and firmware steps instead.

Will error 27 delete my data?

The error itself does not delete anything — it just aborts the restore attempt. However, a restore wipes the iPhone when it completes, and the final DFU-mode step definitely erases everything. Before you go that far, make sure you have a recent iCloud backup or a computer backup you can restore from afterward.

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