Wii system flaws

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This page documents the various bugs in the Wii.


Summary Description Successful exploitation result Fixed in hardware revision Discovered Discovered by
HW_BOOT0 not clear-only To prevent boot0 from being dumped, boot2 clears register HW_BOOT0 that allows the boot0 ROM to be read. However, Nintendo forgot to make this register clear-only, so simply re-enabling it allows boot0 to be dumped from 0xFFFE0000 or 0xFFFF0000 in memory. boot0 can be obtained. Unfixed May 2008 fail0verflow
DVD-Video support is inadequately protected While the Wii was initially meant to support DVD playback, it was scrapped to avoid needing to pay licensing fees. This support was removed in later revisions of the disc drive. However, when the Hollywood register ahbprot is disabled (e.g. by The Homebrew Channel), or diflags is enabled, homebrew can be used to read DVDs. DVDs can be read on the Wii. Unknown July 2008 fail0verflow


Summary Description Successful exploitation result Fixed in boot1 version Discovered Discovered by
strncmp used to compare hashes boot1 verifies the signature of boot2 before booting it, however, the signing bug is present, allowing a fake boot2 to be loaded. A custom bootloader can be installed, such as BootMii. boot1c Unknown fail0verflow


Summary Description Successful exploitation result Fixed in boot2 version Discovered Discovered by
No IOS signature check Unlike boot1, boot2 does not check IOS's signature before launching it, allowing any System Menu IOS to be installed. Any System Menu IOS can be installed. Unfixed Unknown fail0verflow
No System Menu TMD signature check When reading the System Menu TMD, no signature check is done; the IOS number is immediately trusted. A custom System Menu IOS can be installed into a higher slot without overwriting the original IOS. Unfixed Unknown fail0verflow


Module Summary Description Successful exploitation result Fixed in system update Discovered Discovered by
ES Trucha bug The Wii used the strncmp function to check signatures, which always stopped at the first null byte, weakening the security. More information can be found at signing bug. Custom titles can be installed, and fakesigned discs can be played. 3.3 (IOS30 only), October 23 Update (still exploitable by IOS16 pirates), 4.0 Unknown fail0verflow and xt5 (independently)
STM STM release bug The state transition manager checks if a handle is invalid before releasing it, but forgets to actually refuse to release it if it is invalid. More information can be seen at STM Release Exploit Control over IOS can be gained. 4.0 Unknown fail0verflow
ES Title signatures are only checked at installation time. NAND title signatures are checked on install, but never on launch. This means that if a title can be installed, it can be launched without further exploitation. This applies to both IOSes and apps, including the System Menu. One-time exploitation leads to trivial persistence. Unfixed June 2008 fail0verflow
Kernel No sanity checks on arguments passed to wtf1 and wtf2 System calls wtf1 and wtf2 do not check to ensure that the pointers passed are appropriate to write to; they will write to any addresses. If IOS code execution is gained, any address can be overwritten to some specific values by passing those addresses into wtf1 or wtf2. Unknown Unknown fail0verflow
ES No address check in ES_GetTitles One of the parameters of ES_GetTitles is a buffer address for the titles to be written, however, this address is not checked to ensure that it is a Broadway-accessible address. By passing an address to overwrite, the titles fetched will be placed there. Any address accessible from the ES module can be overwritten. Unfixed February 2020 Fullmetal5
ES ES_DiVerify does not check the calling module ES contains no checks when ES_DiVerify is called, responding to any module that calls it. By sending this call from the Broadway over IPC, ES will receive this from the PPCBOOT process, and proceed normally. Homebrew can identify as any title. 4.0 April 2008 fail0verflow and Waninkoko (independently)
ES ES_AddTitleFinish does not check signatures ES_AddTitleFinish does not check the signature of the title passed to ES_AddTitleStart, as it expects the signature to be valid by that point. By switching the title to be installed before calling ES_AddTitleFinish, any title can be installed. Installation of any title 4.3 Unknown Unknown

System Menu

Summary Description Successful exploitation result Fixed in system update Discovered Discovered by
Buffer overflow in mail parser When parsing a message saved to the SD Card, the Wii Message Board has a buffer overflow bug when copying the message body. By overwriting the memory allocation table this way, the next allocation address can be placed on the stack, allowing code to be returned to. LetterBomb and Wilbrand exploit this. Code execution in the System Menu 4.3-U August 2011 fail0verflow and giantpune (independently)
Twilight Hack check only checks one zeldaTp.dat The savefile check to prevent Twilight Hack returns after checking one zeldaTp.dat. By placing a legitimate zeldaTp.dat somewhere else in the file, the real zeldaTp.dat can bypass the check. A new version of the Twilight Hack works. 3.4 June 2008 fail0verflow
Twilight Hack check allows all unaligned zeldaTp.dat sizes The savefile check that prevents Twilight Hack checks the number of bytes read against the file size, aligned to 32 bytes. By leaving the size misaligned, the checker will go past it without deleting it. The new Twilight Hack survives Broadway resets. 3.4 June 2008 fail0verflow
Twilight Hack check only looks at the last zeldaTp.dat file When fixing the 3.3 bugs in the Twilight Hack checker, Nintendo started only checking the final zeldaTp.dat found. By placing a legitimate save later in the WAD, the checker can be bypassed once again. Another Twilight Hack works on 3.4. 4.0 November 2008 fail0verflow


Summary Description Successful exploitation result Fixed in BC version Discovered Discovered by
strncmp used to compare hashes BC verifies the signature of boot2 before booting it, however, the signing bug is present, allowing a fake boot2 to be loaded. If a fakesigned boot2 is installed, GameCube mode will launch it fine. v4 Unknown fail0verflow


Summary Description Successful exploitation result Fixed in MIOS version Discovered Discovered by
Memory not cleared before booting GC game When MIOS loads a GameCube game, it never clears the 48K bytes of memory that the game should not have access to. By using a pair of tweezers to change the address lines, the entire memory can be dumped. MIOS and the rest of memory can be dumped using GameCube homebrew. v8 Unknown fail0verflow
No boot2 signature check When the power button is pressed in GameCube mode, MIOS loads boot2 in a shutdown state. However, it has no signature verification, so it is easy to reboot into software such as BootMii this way. The Wii will not hang on shutdown from MIOS if a customer boot2 is installed. Unfixed Unknown fail0verflow

Nintendo SDK

These flaws exist in every official application, because they are bundled in, probably in the official SDK. For this reason, they are very difficult to fix.

Summary Description Successful exploitation result Discovered Discovered by
No upper bound to CCB array The Fluoride Bluetooth stack includes a function to get a CCB from an ID. This function checks whether the ID is below the lower bound, however, no upper bound is enforced.

By carefully crafting an ID, a fake CCB entry can be placed in the handles array. Sending a packet to free this struct causes it to "unlink" from its adjacent entries, which can be used to get an arbitrary write, and therefore code execution.

PPC code execution (used in Bluebomb) September 2019 Fullmetal5
No size limit to BigInts in Opera In Opera, the dtoa module includes a number of functions operating on big integers with a maximum size, however, any sizes passed in are never checked. By passing in a value too large, the BigInt allocation table will return a smaller BigInt, which leads to a buffer overflow. PPC code execution (used in str2hax) December 2018 Fullmetal5
Use-after-free in Flash objects Flash includes a feature to watch certain properties and get notified when they change, with the ability to easily change it again by returning a value from the event handler. If the event handler decides to delete the object holding that property, the caller still sets the value at that address.

With some manipulation of the garbage collector and thread-switching systems, the stack pointer can be changed, allowing ROP to begin.

ROP in the PPC (used in FlashHax) March 2018 Fullmetal5