近期学习ios逆向，也为了熟悉一下iOS开发正向。用objective-c整了一个越狱检测的crackme，然后用frida过一遍自己写的检测（真是没事找事）。代码粗糙，请见谅。
准备
克隆项目，再用xcode安装到手机上
使用stat检测敏感路径
利用stat检查一些越狱后才有的敏感路径，如：/Applications/Cydia.app 和 /usr/sbin/sshd，以此来判断是否越狱。stat判断文件是否存在, 返回0则为获取成功，-1为获取失败。可通过hook stat，过掉检测
function hook_stat(is_pass){
var stat = Module.findExportByName('libSystem.B.dylib', 'stat');
Interceptor.attach(stat, {
onEnter: function(args) {
// 这里是方法被调用时的处理逻辑
// args[0] 是 stat 方法的第一个参数，通常是文件路径
// args[1] 是 stat 方法的第二个参数，这里可以添加其他参数的处理
console.log('stat is hooked: ');
},
onLeave: function(retval){
if (is_pass){
retval.replace(-1);
console.log(`stat retval: ${Number(retval.toString())} -> -1`);
}
}
});
}
检查dylib是否合法
越狱后会产生一些特殊的链接库，ipa可以通过_dyld_get_image_name来获取所有的链接库，再遍历匹配，判断是否为越狱设备。
可以通过分析找到ipa检测的dylib，再hook _dyld_get_image_name，将返回替换为合法dylib，过掉检测。
function hook_dyld_get_image_name(is_pass){
let cheek_paths = [
"/Library/MobileSubstrate/MobileSubstrate.dylib",
]
let NSString = ObjC.classes.NSString;
let true_path = NSString.stringWithString_( "/System/Library/Frameworks/Intents.framework/Intents");
let _dyld_get_image_name = Module.findExportByName(null, "_dyld_get_image_name");
Interceptor.attach(_dyld_get_image_name, {
onEnter: function(args){
console.log("_dyld_get_image_name is hooked.")
this.idx = eval(args[0]).toString(10);
},
onLeave: function(retval){
let rtnStr = retval.readCString();
if(is_pass){
for (let i=0;i ${true_path}`)
}
}
}
}
})
}
检测能否启动越狱app
越狱后会在手机上安装越狱设备，如cydia。可以通过 -[UIApplication canOpenURL:] 来检测是否能启动app。
可hook -[UIApplication canOpenURL:] 替换返回过掉检测。但canOpenURL方法 返回是个 BOOL，即YES/NO，也就是1和0的宏。但在Interceptor.attach里用 retval.replace()总是会导致app崩溃（不知道原理，望大佬指点）。
所以使用 Interceptor.replace() + NaviteCallback, 替换掉方法，使其固定返回 0,也就是 NO。但这个解法，也不能算是好方法。。。
function hook_canopenurl(is_pass){
let api = new ApiResolver("objc");
api.enumerateMatches("-[UIApplication canOpenURL:]").forEach((matche) => {
console.log("canOpenURL is hooked.");
if (is_pass){
Interceptor.replace(matche.address, new NativeCallback((url_obj) => {return 0;}, "int", ["pointer"]))
}
})
}
检测越狱文件和目录
越狱后会产生特殊的文件和目录，可以通过 fileExistsAtPath 来检测，直接hook过掉
// -[NSFileManager fileExistsAtPath:isDirectory:]
function hook_fileExistsAtPath(is_pass){
let api = new ApiResolver("objc");
let matches = api.enumerateMatches("-[NSFileManager fileExistsAtPath:isDirectory:]")
matches.forEach((matche) => {
console.log("fileExistsAtPath is hooked.");
if(is_pass){
Interceptor.replace(matche.address, new NativeCallback((path, is_dir) => {
console.log(ObjC.Object(path).toString(), is_dir)
return 0;
}, "int", ["pointer", "bool"]))
}
})
}
检测是否可写私有路径权限
越狱后为root权限，可以在私有路径如 /private/ 下创建文件。如果创建文件无异常则越狱，反之。
可通过 ObjC.classes.NSError.alloc() 构建一个异常写入ipa检测的异常指针中
function hook_writeToFile(is_pass){
let api = new ApiResolver("objc");
api.enumerateMatches("-[NSString writeToFile:atomically:encoding:error:]").forEach((matche) => {
Interceptor.attach(matche.address, {
onEnter: function(args){
this.error = args[5];
this.path = ObjC.Object(args[2]).toString();
console.log("writeToFile is hooked");
},
onLeave: function(retval){
if(is_pass){
let err = ObjC.classes.NSError.alloc();
Memory.writePointer(this.error, err);
}
}
})
})
}
检测文件路径和是否是路径链接
越狱后有些文件会被移动，但这个文件路径又必须存在，所以可能会创一个文件链接。ipa可以检测一些敏感路径是否是链接来判断是否越狱。
这里仅过掉路径检测（符号链接不会过T.T）
// oc 检测函数
+ (Boolean)isLstatAtLnk{
// 检测文件路径是否存在，是否是路径链接
Boolean result = FALSE;
NSArray* jbPaths = @[
@"/Applications",
@"/var/stash/Library/Ringtones",
@"/var/stash/Library/Wallpaper",
@"/var/stash/usr/include",
@"/var/stash/usr/libexec",
@"/var/stash/usr/share",
@"/var/stash/usr/arm-apple-darwin9",
];
struct stat stat_info;
for(NSString* jbPath in jbPaths){
char jbPathChar[jbPath.length];
memcpy(jbPathChar, [jbPath cStringUsingEncoding:NSUTF8StringEncoding], jbPath.length);
if (lstat(jbPathChar, &stat_info)){
NSLog(@"stat_info.st_mode: %hu, S_IFLNK: %d, %d", stat_info.st_mode, S_IFLNK, stat_info.st_mode & S_IFLNK);
if(stat_info.st_mode & S_IFLNK){
result = TRUE;
NSLog(@"是路径链接>> %@", jbPath);
}
}else{
NSLog(@"路径不存在>> %@", jbPath);
result = TRUE;
}
}
return result;
}
// 过lstat
function hook_lstat(is_pass){
var stat = Module.findExportByName('libSystem.B.dylib', 'lstat');
Interceptor.attach(stat, {
onEnter: function(args) {
console.log('lstat is hooked: ');
},
onLeave: function(retval){
if (is_pass){
retval.replace(1);
console.log(`lstat retval: ${Number(retval.toString())} -> 1`);
}
}
});
}
检测fork
未越狱的设备是无法fork子进程
hook fork
function hook_fork(is_pass){
let fork = Module.findExportByName(null, "fork");
if (fork){
console.log("fork is hooked.");
Interceptor.attach(fork, {
onLeave: function(retval){
console.log(`fork -> pid:${retval}`);
if(is_pass){
retval.replace(-1)
}
}
})
}
}
检测越狱常用的类
查看是否有注入异常的类,比如HBPreferences 是越狱常用的类，再用 NSClassFromString 判断类是否存在
通过分析找出检测的类名，再去hook NSClassFromString
function hook_NSClassFromString(is_pass){
let clses = ["HBPreferences"];
var foundationModule = Process.getModuleByName('Foundation');
var nsClassFromStringPtr = Module.findExportByName(foundationModule.name, 'NSClassFromString');
if (nsClassFromStringPtr){
Interceptor.attach(nsClassFromStringPtr, {
onEnter: function(args){
this.cls = ObjC.Object(args[0])
console.log("NSClassFromString is hooked");
},
onLeave: function(retval){
if (is_pass){
clses.forEach((ck_cls) => {
if (this.cls.toString().indexOf(ck_cls) !== -1){
console.log(`nsClassFromStringPtr -> ${this.cls} - ${ck_cls}`)
retval.replace(ptr(0x00))
}
})
}
}
})
}
}
检测是否有环境变量
通过getenv函数，查看环境变量DYLD_INSERT_LIBRARIES来检测是否越狱
hook getenv
function hook_getenv(is_pass){
let getenv = Module.findExportByName(null, "getenv");
Interceptor.attach(getenv, {
onEnter: function(args){
console.log("getenv is hook");
this.env = ObjC.Object(args[0]).toString();
},
onLeave: function(retval){
if (is_pass && this.env == "DYLD_INSERT_LIBRARIES"){
console.log(`env: ${this.env} - ${retval.readCString()}`)
retval.replace(ptr(0x0))
}
}
})
}
整体代码
function hook_stat(is_pass){
var stat = Module.findExportByName('libSystem.B.dylib', 'stat');
Interceptor.attach(stat, {
onEnter: function(args) {
// 这里是方法被调用时的处理逻辑
// args[0] 是 stat 方法的第一个参数，通常是文件路径
// args[1] 是 stat 方法的第二个参数，这里可以添加其他参数的处理
console.log('stat is hooked: ');
},
onLeave: function(retval){
if (is_pass){
retval.replace(-1);
console.log(`stat retval: ${Number(retval.toString())} -> -1`);
}
}
});
}
function hook_dyld_get_image_name(is_pass){
let cheek_paths = [
"/Library/MobileSubstrate/MobileSubstrate.dylib",
]
let NSString = ObjC.classes.NSString;
let true_path = NSString.stringWithString_( "/System/Library/Frameworks/Intents.framework/Intents");
let _dyld_get_image_name = Module.findExportByName(null, "_dyld_get_image_name");
Interceptor.attach(_dyld_get_image_name, {
onEnter: function(args){
console.log("_dyld_get_image_name is hooked.")
this.idx = eval(args[0]).toString(10);
},
onLeave: function(retval){
let rtnStr = retval.readCString();
if(is_pass){
for (let i=0;i ${true_path}`)
}
}
}
}
})
}
function hook_canopenurl(is_pass){
let api = new ApiResolver("objc");
api.enumerateMatches("-[UIApplication canOpenURL:]").forEach((matche) => {
console.log("canOpenURL is hooked.");
if (is_pass){
Interceptor.replace(matche.address, new NativeCallback((url_obj) => {return 0;}, "int", ["pointer"]))
}
})
}
// -[NSFileManager fileExistsAtPath:isDirectory:]
function hook_fileExistsAtPath(is_pass){
let api = new ApiResolver("objc");
let matches = api.enumerateMatches("-[NSFileManager fileExistsAtPath:isDirectory:]")
matches.forEach((matche) => {
console.log("fileExistsAtPath is hooked.");
if(is_pass){
Interceptor.replace(matche.address, new NativeCallback((path, is_dir) => {
console.log(ObjC.Object(path).toString(), is_dir)
return 0;
}, "int", ["pointer", "bool"]))
}
})
}
function hook_writeToFile(is_pass){
let api = new ApiResolver("objc");
api.enumerateMatches("-[NSString writeToFile:atomically:encoding:error:]").forEach((matche) => {
Interceptor.attach(matche.address, {
onEnter: function(args){
this.error = args[5];
this.path = ObjC.Object(args[2]).toString();
console.log("writeToFile is hooked");
},
onLeave: function(retval){
if(is_pass){
let err = ObjC.classes.NSError.alloc();
Memory.writePointer(this.error, err);
}
}
})
})
}
function hook_lstat(is_pass){
var stat = Module.findExportByName('libSystem.B.dylib', 'lstat');
Interceptor.attach(stat, {
onEnter: function(args) {
console.log('lstat is hooked: ');
},
onLeave: function(retval){
if (is_pass){
retval.replace(1);
console.log(`lstat retval: ${Number(retval.toString())} -> 1`);
}
}
});
}
function hook_fork(is_pass){
let fork = Module.findExportByName(null, "fork");
if (fork){
console.log("fork is hooked.");
Interceptor.attach(fork, {
onLeave: function(retval){
console.log(`fork -> pid:${retval}`);
if(is_pass){
retval.replace(-1)
}
}
})
}
}
function hook_NSClassFromString(is_pass){
let clses = ["HBPreferences"];
var foundationModule = Process.getModuleByName('Foundation');
var nsClassFromStringPtr = Module.findExportByName(foundationModule.name, 'NSClassFromString');
if (nsClassFromStringPtr){
Interceptor.attach(nsClassFromStringPtr, {
onEnter: function(args){
this.cls = ObjC.Object(args[0])
console.log("NSClassFromString is hooked");
},
onLeave: function(retval){
if (is_pass){
clses.forEach((ck_cls) => {
if (this.cls.toString().indexOf(ck_cls) !== -1){
console.log(`nsClassFromStringPtr -> ${this.cls} - ${ck_cls}`)
retval.replace(ptr(0x00))
}
})
}
}
})
}
}
function hook_getenv(is_pass){
let getenv = Module.findExportByName(null, "getenv");
Interceptor.attach(getenv, {
onEnter: function(args){
console.log("getenv is hook");
this.env = ObjC.Object(args[0]).toString();
},
onLeave: function(retval){
if (is_pass && this.env == "DYLD_INSERT_LIBRARIES"){
console.log(`env: ${this.env} - ${retval.readCString()}`)
retval.replace(ptr(0x0))
}
}
})
}
setImmediate(() => {
hook_stat(true);
hook_dyld_get_image_name(true)
hook_canopenurl(true);
hook_fileExistsAtPath(true);
hook_writeToFile(true);
hook_lstat(true);
hook_fork(true);
hook_NSClassFromString(true);
hook_getenv(true)
})
小结
检测的正向代码在项目的 JailBreakCheek 类下。单独过这些检测基本没啥难度，直接hook。但在真实app中还是重点在分析中，如何找到这些具体检测的点。这次分享的frida代码有点粗糙，啊哈哈，要实际使用还得再优化一下。并且可以多看看frida官方的脚本网站https://codeshare.frida.re/
后面有时间的话，再分享些其他类型的检测如frida检测，混淆代码或加固之类。
文章参考
