Flutter抓包绕过

起因：

最近工作上让做个app的复测，把apk发我后，开始尝试挂代理抓包，结果发现抓不到。

以为是证书没弄好，想着前几天不是刚导入了吗（雾）。又重新导入了下还是不行。然后各种lsp模块，objection都不行，r0capture也没数据。

然后jadx看了下，全是flutter字样，才想起来和flutter有关。

然后就开始各种找，https://bbs.kanxue.com/thread-261941.htm

根据上面文章找到关键函数handshake.cc（https://github.com/google/boringssl/blob/master/ssl/handshake.cc）386行：

session_verify_cert_chain函数在第356行的ssl_x509.cc（https://github.com/google/boringssl/blob/master/ssl/ssl_x509.cc）中被定义：

然后根据https://bbs.kanxue.com/thread-261941.htm这篇文章特征找，但是这个是32位的，所以在app安装的时候指定32位安装。

adb install --abi armeabi-v7a <path to apk>

接下来就是找：

往上翻找：

2 写脚本绕过

32位

function hook_ssl_verify_result(address) {
Interceptor.attach(address, {
        onEnter: function(args) {
            console.log("Disabling SSL validation")
        },
        onLeave: function(retval) {
            console.log("Retval: " + retval);
            retval.replace(0x1);
        }
    }); 
}
function hookFlutter() {
    var m = Process.findModuleByName("libflutter.so");
    var pattern = "2D E9 F0 4F 85 B0 06 46 50 20 10 70";
    var res = Memory.scan(m.base, m.size, pattern, {
        onMatch: function(address, size){
            console.log('[+] ssl_verify_result found at: ' + address.toString());
        // Add 0x01 because it's a THUMB function
        // Otherwise, we would get 'Error: unable to intercept function at 0x9906f8ac; please file a bug'
            hook_ssl_verify_result(address.add(0x01)); 
        },
        onError: function(reason){
            console.log('[!] There was an error scanning memory');
        },
        onComplete: function() {
            console.log("All done")
        }
    });
}

然后启动就可以抓包了：

64位

搜索ssl_client：

照例往上找:

然后就找到了这些:

.text:0000000000596870 FF C3 01 D1                 SUB             SP, SP, #0x70
.text:0000000000596874 FD 7B 01 A9                 STP             X29, X30, [SP,#0x70+var_60]
.text:0000000000596878 FC 6F 02 A9                 STP             X28, X27, [SP,#0x70+var_50]
.text:000000000059687C FA 67 03 A9                 STP             X26, X25, [SP,#0x70+var_40]
.text:0000000000596880 F8 5F 04 A9                 STP             X24, X23, [SP,#0x70+var_30]
.text:0000000000596884 F6 57 05 A9                 STP             X22, X21, [SP,#0x70+var_20]
.text:0000000000596888 F4 4F 06 A9                 STP             X20, X19, [SP,#0x70+var_10]
.text:000000000059688C 08 0A 80 52                 MOV             W8, #0x50
.text:0000000000596890 48 00 00 39                 STRB            W8, [X2]

然后写脚本:

function hook_ssl_verify_result(address) {
Interceptor.attach(address, {
        onEnter: function(args) {
            console.log("Disabling SSL validation")
        },
        onLeave: function(retval) {
            console.log("Retval: " + retval);
            retval.replace(0x1);
        }
    }); 
}
function hookFlutter() {
    var m = Process.findModuleByName("libflutter.so");
    var pattern = "FF C3 01 D1 FD 7B 01 A9 FC 6F 02 A9FA 67 03 A9 F8 5F 04 A9 F6 57 05 A9 F4 4F 06 A9 08 0A 80 52 48 00 00 39";
    var res = Memory.scan(m.base, m.size, pattern, {
        onMatch: function(address, size){
            console.log('[+] ssl_verify_result found at: ' + address.toString());
        // Add 0x01 because it's a THUMB function
        // Otherwise, we would get 'Error: unable to intercept function at 0x9906f8ac; please file a bug'
            hook_ssl_verify_result(address.add(0x01)); 
        },
        onError: function(reason){
            console.log('[!] There was an error scanning memory');
        },
        onComplete: function() {
            console.log("All done")
        }
    });
}

然后发现报错了:

把hook_ssl_verify_result(address.add(0x01))改为hook_ssl_verify_result(address)就可以正常使用了:

3 参考资料

1. https://www.jianshu.com/p/ada10d2976f2
2. https://mp.weixin.qq.com/s/pXpfXK-Ez0n70f3bqFuuFg
3. https://bbs.kanxue.com/thread-261941.htm
4. https://blog.nviso.eu/2019/08/13/intercepting-traffic-from-android-flutter-applications/

以上四篇文章均是和flutter证书校验相关。