3dbrew

3DS System Flaws

Page Discussion
Revision as of 20:39, 9 March 2015 by Yellows8 (talk | contribs) (→‎Process9)

Exploits are used to execute unofficial code (homebrew) on the Nintendo 3DS. This page is a list of known 3DS-mode exploits.

List of public 3DS exploits

  • See here regarding Ninjhax.

Stale / Rejected Efforts

  • Neimod has been working on a RAM dumping setup for a little while now. He's de-soldered the 3DS's RAM chip and hooked it and the RAM pinouts on the 3DS' PCB up to a custom RAM dumping setup. A while ago he published photos showing his setup to be working quite well, with the 3DS successfully booting up. However, his flickr stream is now private along with most of his work.
  • Someone (who will remain unnamed) has released CFW and CIA installers, all of which is copied from the work of others, or copyrighted material.

Failed attempts

Here are listed all attempts at exploiting 3DS software that have failed so far.

  • Pushmo (3DSWare), QR codes: level name is properly limited to 16 characters, game doesn't crash with a longer name. The only possible crashes are triggered by out-of-bounds array index values, these crashes are not exploitable.


  • Pyramids (3DSWare), QR codes: no strings. Only crashes are from out-of-bounds values (like background ID) and are not exploitable.


  • 3DS browser, 2^32 characters long string: this is similar to the vulnerability fixed here, concat-large-strings-crash2.html triggers a crash which is about the same as the one triggered by a 2^32 string. Most of the time this vulnerability will cause a memory page permissions fault, since the WebKit code attempts to copy the string text data to the output buffer located in read-only CRO heap memory. The only difference between a crash triggered by a 2^32 string and the concat-large-strings-crash2.html crash is at the former copies the string data using the original string length(like 1 text character for "x", 4 for "xxxx") while the latter attempts to copy >12MB. In some very rare cases a thread separate from the string data-copy thread will crash, this might be exploitable. However, this is mostly useless since it rarely crashes this way.

Tips and info

The 3DS uses the XN feature of the ARM11 processor. There's no official way from applications to enable executable permission for memory containing arbitrary unsigned code(there's a SVC for this, but only RO-module has access to it). An usable userland exploit would still be useful: you could only do return-oriented-programming with it initially. From ROP one could then exploit system flaw(s), see below.

SD card extdata and SD savegames can be attacked, for consoles where the console-unique movable.sed was dumped(accessing SD data is far easier by running code on the target 3DS however).

Note that the publicly-available <v5.0 total-control exploits are Process9 exploits, not "kernel exploits".

System flaws

TWL_FIRM

Process9

Summary Description Successful exploitation result Fixed in FIRM system version Last FIRM system version this flaw was checked for Timeframe this was discovered Discovered by
TWL RSA signature padding checks The TWL_FIRM RSA sig padding check code used for all TWL RSA sig-checks has issues, see here. None Old3DS: 6.2.0-12. New3DS: 8.1.0-0_New3DS Yellows8

FIRM Process9

Summary Description Successful exploitation result Fixed in FIRM system version Last FIRM system version this flaw was checked for Timeframe this was discovered Discovered by
Uncleared New3DS keyslot 0x11 Originally the New3DS FIRM arm9bin loader only cleared keyslot 0x11 when it gets executed at firmlaunch. This was fixed with 9.5.0-X by completely clearing keyslot 0x11 immediately after the loader finishes using keyslot 0x11.

This means that any ARM9 code that can execute before the loader clears the keyslot at firmlaunch(including firmlaunch-hax) can get access to the uncleared keyslot 0x11, which then allows one to generate all <=v9.5 New3DS keyXs which are generated by keyslot 0x11.

Therefore, to completely fix this the loader would have to generate more keys using different keyslot 0x11 keydata.

New3DS keyXs generation 9.5.0-X February 3, 2015 (one day after 9.5.0-X release) Yellows8
firmlaunch-hax: FIRM header ToCToU This can't be exploited from ARM11 userland.

During FIRM launch, the only FIRM header the ARM9 uses at all is stored in FCRAM, this is 0x200-bytes(the actual used FIRM RSA signature is read to the Process9 stack however). The ARM9 doesn't expect "anything" besides the ARM9 to access this data. With 9.5.0-22 the address of this FIRM header was changed from a FCRAM address, to ARM9-only address 0x01fffc00.

ARM9 code execution 9.5.0-22 2012, 3 days after Yellows8 started Process9 code RE. Yellows8
Uninitialized data output for PXI command replies Various (stubbed?) PXI commands(including some here) just write uninitialized data (like from ARM registers) to the command reply. None 9.3.0-X ? Yellows8
FSPXI OpenArchive SD permissions Process9 does not use the exheader ARM9 access-mount permission flag for SD at all.

This would mean ARM11-kernelmode code / fs-module itself could directly use FSPXI to access SD card without ARM9 checking for SD access, but this is rather useless since a process is usually running with SD access(Home Menu for example) anyway.

None 9.3.0-X 2012 Yellows8
Gamecard_Services_PXI unchecked REG_CTRCARDCNT transfer-size The u8 REG_CTRCARDCNT transfer-size parameter for the Gamecard_Services_PXI read/write CTRCARD commands is used as an index for an array of u16 values. Before 5.0.0-X this u8 value wasn't checked, thus out-of-bounds reads could be triggered(which is rather useless in this case). Out-of-bounds read for a value which gets written to a register. 5.0.0-X 2013? Yellows8
PXIAM command 0x003D0108(See also this) When handling this command, Process9 allocates a 0x2800-byte heap buffer, then copies the 4 FCRAM input buffers to this heap buffer without checking the sizes at all(only the buffers with non-zero sizes are copied). Starting with 5.0.0-X, the total combined size of the input data must be <=0x2800. ARM9 code execution 5.0.0-X May 2013 Yellows8
PS RSA commands buffer overflows pxips9 cmd1(not accessible via ps:ps) and VerifyRsaSha256: unchecked copy to a buffer in Process9's .bss, from the input FCRAM buffer. The buffer is located before the pxi cmdhandler threads' stacks. SignRsaSha256 also has a buf overflow, but this isn't exploitable.

The buffer for this is the buffer for the signature data. With v5.0, the signature buffer was moved to stack, with a check for the signature data size. When the signature data size is too large, Process9 uses svcBreak.

ARM9 code execution 5.0.0-X 2012 Yellows8

ARM11 kernel

Summary Description Successful exploitation result Fixed in FIRM system version Last FIRM system version this flaw was checked for Timeframe this was discovered Discovered by
SVC table too small The table of function pointers for SVC's only contains entries up to 0x7D, but the biggest allowed SVC for the table is 0x7F. Thus, executing SVC7E or SVC7F would make the SVC-handler read after the buffer, and interpret some ARM instructions as function pointers.

However, this would require patching the kernel .text or modifying SVC-access-control. Even if you could get these to execute, they would still jump to memory that isn't mapped as executable.

None 9.5.0-X 2012 Everyone
svcBackdoor (0x7B) This backdoor allows executing SVC-mode code at the user-specified code-address. This is used by Process9, using this on the ARM11(with NATIVE_FIRM) requires patching the kernel .text or modifying SVC-access-control. See description None 9.5.0-X Everyone
0xEFF00000 / 0xDFF00000 ARM11 kernel virtual-memory The ARM11 kernel-mode 0xEFF00000/0xDFF00000 virtual-memory(size 0x100000) is mapped to phys-mem 0x1FF00000(entire DSP-mem + entire AXIWRAM), with permissions RW-. This is used during ARM11 kernel startup, this never seems to be used after that, however. None 9.5.0-X
memchunkhax The kernel originally did not validate the data stored in the FCRAM kernel heap memchunk-headers for free-memory at all. Exploiting this requires raw R/W access to these memchunk-headers, like physical-memory access with gspwn.

There are multiple ways to exploit this, but the end-result for most of these is the same: overwrite code in AXIWRAM via the 0xEFF00000/0xDFF00000 kernel virtual-memory mapping.

This was fixed in 9.3.0-X by checking that the memchunk(including size, next, and prev ptrs) is located within the currently used heap memory. The kernel may also check that the next/prev ptrs are valid compared to other memchunk-headers basically. When any of these checks fail, kernelpanic() is called.

When combined with other flaws: ARM11-kernelmode code execution 9.3.0-21 February 2014 Yellows8
PXI Command input/output buffer permissions Originally the ARM11-kernel didn't check permissions for PXI input/output buffers for commands. Starting with 6.0.0 PXI input/output buffers must have RW permissions, otherwise kernelpanic is triggered. 6.0.0-11 2012 Yellows8
svcStartInterProcessDma For svcStartInterProcessDma, the kernel code had the following flaws:
  • Originally the ARM11-kernel read the input DmaConfig structure directly in kernel-mode(ldr(b/h) instructions), without checking whether the DmaConfig address is readable under userland. This was fixed by copying that structure to the SVC-mode stack, using the ldrbt instruction.
  • Integer overflows for srcaddr+size and dstaddr+size are now checked(with 6.0.0-11), which were not checked before.
  • The kernel now also checks whether the srcaddr/dstaddr (+size) is within userland memory (0x20000000), the kernel now (with 6.0.0-11) returns an error when the address is beyond userland memory. Using an address >=0x20000000 would result in the kernel reading from the process L1 MMU table, beyond the memory allocated for that MMU table(for vaddr->physaddr conversion).
 6.0.0-11 DmaConfig issue: unknown. The rest: 2014 plutoo, Yellows8 independently
svcControlMemory Parameter checks For svcControlMemory the parameter check had these two flaws:
  • The allowed range for addr0, addr1, size parameters depends on which MemoryOperation is being specified. The limitation for GSP heap was only checked if op=(u32)0x10003. By setting a random bit in op that has no meaning (like bit17?), op would instead be (u32)0x30003, and the range-check would be less strict and not accurate. However, the kernel doesn't actually use the input address for LINEAR memory-mapping at all besides the range-checks, so this isn't actually useful. This was fixed in the kernel by just checking for the LINEAR bit, instead of comparing the entire MemoryOperation value with 0x10003.
  • Integer overflows on (addr0+size) are now checked that previously weren't (this also applies to most other address checks elsewhere in the kernel).
 5.0.0-11 plutoo
Command request/response buffer overflow Originally the kernel did not check the word-values from the command-header. Starting with 5.0.0-11, the kernel will trigger a kernelpanic() when the total word-size of the entire command(including the cmd-header) is larger than 0x40-words (0x100-bytes). This allows overwriting threadlocalstorage+0x180 in the destination thread. However, since the data written there would be translate parameters (such as header-words + buffer addresses), exploiting this would likely be very difficult, if possible at all.

If the two words at threadlocalstorage+0x180 could be overwritten with controlled data this way, one could then use a command with a buffer-header of ((size<<14) | 2) to write arbitrary memory to any RW userland memory in the destination process.

5.0.0-11 v4.1 FIRM -> v5.0 code diff Yellows8
SVC stack allocation overflows
  • Syscalls that allocate a variable-length array on stack, only checked bit31 before multiplying by 4/16 (when calculating how much memory to allocate). If a large integer was passed as input to one of these syscalls, an integer overflow would occur, and too little memory would have been allocated on stack resulting in a buffer overrun.
  • The alignment (size+7)&~7 calculation before allocation was not checked for integer overflow.

This might allow for ARM11 kernel code-execution.

(Applies to svcSetResourceLimitValues, svcGetThreadList, svcGetProcessList, svcReplyAndReceive, svcWaitSynchronizationN.)

5.0.0-11 v4.1 FIRM -> v5.0 code diff plutoo, Yellows8 complementary
svcControlMemory MemoryOperation MAP memory-permissions svcControlMemory with MemoryOperation=MAP allows mapping the already-mapped process virtual-mem at addr1, to addr0. The lowest address permitted for addr1 is 0x00100000. Originally the ARM11 kernel didn't check memory permissions for addr1. Therefore .text as addr1 could be mapped elsewhere as RW- memory, which allowed ARM11 userland code-execution. 4.1.0-8 2012 Yellows8
Command input/output buffer permissions Originally the ARM11 kernel didn't check memory permissions for the input/output buffers for commands. Starting with 4.0.0-7 the ARM11 kernel will trigger a kernelpanic() if the input/output buffers don't have the required memory permissions. For example, this allowed a FSUSER file-read to .text, which therefore allowed ARM11-userland code execution. 4.0.0-7 2012 Yellows8
svcReadProcessMemory/svcWriteProcessMemory memory permissions Originally the kernel only checked the first page(0x1000-bytes) of the src/dst buffers, for svcReadProcessMemory and svcWriteProcessMemory. There is no known retail processes which have access to these SVCs. 4.0.0-7 2012? Yellows8

FIRM ARM11 modules

Summary Description Successful exploitation result Fixed in FIRM system version Last FIRM system version this flaw was checked for Timeframe this was discovered Discovered by
"srv:pm" process registration Originally any process had access to the port "srv:pm". The PID's used for the (un)registration commands are not checked either. This allowed any process to re-register itself with "srv:pm", and therefore allowed the process to give itself access to any service, bypassing the exheader service-access-control list.

This was fixed in 7.0.0-13: starting with 7.0.0-13 "srv:pm" is now a service instead of a globally accessible port. Only processes with PID's less than 6 (in other words: fs, ldr, sm, pm, pxi modules) have access to it. With 7.0.0-13 there can only be one session for "srv:pm" open at a time(this is used by pm module), svcBreak will be executed if more sessions are opened by the processes which can access this.

This flaw was needed for exploiting the <=v4.x Process9 PXI vulnerabilities from ARM11 userland ROP, since most applications don't have access to those service(s).

Access to arbitrary services 7.0.0-13 2012 Yellows8

ARM11 system modules

Summary Description Successful exploitation result Fixed in system version Last system version this flaw was checked for Timeframe this was discovered Discovered by
gspwn GSP module does not validate addresses given to the GPU. This allows a user-mode application/applet to read/write to a large part of physical FCRAM using GPU DMA. From this, you can overwrite the .text segment of the application you're running under, and gain real code-execution from a ROP-chain. Normally applets' .text(Home Menu, Internet Browser, etc) is located beyond the area accessible by the GPU, except for CROs used by applets(Internet Browser for example). User-mode code execution. None 9.5.0-22 Early 2014 smea, Yellows8/others before then
rohax Using gspwn, it is possible to overwrite a loaded CRO0/CRR0 after its RSA-signature has been validated. Badly validated CRO0 header leads to arbitrary read/write of memory in the ro-process. This gives code-execution in the ro module, who has access to syscalls 0x70-0x72, 0x7D.

This was fixed after ninjhax release by adding checks on CRO0-based pointers before writing to them.

Memory-mapping syscalls. 9.3.0-21 9.4.0-21 smea, plutoo joint effort
Region free Only Home Menu itself checks gamecards' region when launching them. Therefore, any application launch that is done directly with NS without signaling Home Menu to launch the app, will result in region checks being bypassed.

This essentially means launching the gamecard with the "ns:s" service. The main way to exploit this is to trigger a FIRM launch with an application specified, either with a normal FIRM launch or a hardware reboot.

Launching gamecards from any region + bypassing Home Menu gamecard-sysupdate installation None 9.5.0-22 June(?) 2014 Yellows8

ARM11 system applications and applets

Summary Description Successful exploitation result Fixed in system version Last system version this flaw was checked for Timeframe this was discovered Discovered by
3DS System Settings DS profile string stack-smash Too long or corrupted strings (01Ah 2 Nickname length in characters 050h 2 Message length in characters) in the NVRAM DS user settings (System Settings->Other Settings->Profile->Nintendo DS Profile) cause it to crash in 3DS-mode due to a stack-smash. The DSi is not vulnerable to this, DSi launcher(menu) and DSi System Settings will reset the NVRAM user-settings if the length field values are too long(same result as when the CRCs are invalid). TWL_FIRM also resets the NVRAM user-settings when the string-length(s) are too long. ROP in mset. 7.0.0-13 7.0.0-13 2012 Ichfly

General/CTRSDK

Summary Description Successful exploitation result Fixed in version Last version this flaw was checked for Timeframe this was discovered Discovered by
UDS beacon additional-data buffer overflow Originally CTRSDK did not validate the UDS additional-data size before using that size to copy the additional-data to a networkstruct. This was eventually fixed.

This was discovered while doing code RE with an old dlp-module version. It's unknown in what specific CTRSDK version this was fixed, or even what system-version updated titles with a fixed version.

It's unknown if there's any titles using a vulnerable CTRSDK version which are also exploitable with this(dlp module can't be exploited with this).

The maximum number of bytes that can be written beyond the end of the outbuf is 0x37-bytes, with additionaldata_size=0xFF.

Perhaps ROP, very difficult if possible with anything at all ? September(?) 2014 Yellows8
Retrieved from "https://www.3dbrew.org/w/index.php?title=3DS_System_Flaws&oldid=11877"