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Inspecting iOS App Traffic with JavaScript
@AndyDavies
https://www.flickr.com/photos/marc-flores/8367323660
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WHY?
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DEMO
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http://www.delaat.net/rp/2015-2016/p52/report.pdf
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Inject JavaScript into an App!
https://www.frida.re/
App
JavaScript VM
Script
Host
Injects script
Receives Messages
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https://opensource.apple.com/source/coreTLS/coreTLS-83.20.8/lib/tls1Callouts.c.auto.html
/*
* The TLS pseudorandom function, defined in RFC2246, section 5.
* This takes as its input a secret block, a label, and a seed, and produces
* a caller-specified length of pseudorandom data.
*
* Optimization TBD: make label optional, avoid malloc and two copies if it's
* not there, so callers can take advantage of fixed-size seeds.
*/
// Note: This is exported as SPI.
int tls_handshake_internal_prf(
tls_handshake_t ctx,
const void *vsecret,
size_t secretLen,
const void *label, // optional, NULL implies that seed contains
// the label
size_t labelLen,
const void *seed,
size_t seedLen,
void *vout, // mallocd by caller, length >= outLen
size_t outLen)
{
int serr = errSSLInternal;
…
Master Secret
Client & Server
Randoms
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var hexChar = ["0", "1", "2", "3", "4", "5", "6", "7","8", "9", "A", "B", "C", "D", "E", "F"];
function byteToHex(byte) {
return hexChar[(byte >> 4) & 0x0f] + hexChar[byte & 0x0f];
}
var f = Module.findExportByName("libsystem_coretls.dylib", "tls_handshake_internal_prf");
Interceptor.attach(f, {onEnter: function (args) {
var secretLength = parseInt(args[2], 16);
var seedLength = parseInt(args[6], 16);
if(secretLength == 48 && (seedLength == 64 || seedLength == 77)) {
var secretAddr = new NativePointer(args[1])
var secretBytes = new Uint8Array(Memory.readByteArray(secretAddr, secretLength));
var secret = "";
for(var i = 0; i < secretLength; i++) {
secret += byteToHex(secretBytes[i]);
}
Find function
Hook function
Extract master secret
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var seedLength = parseInt(args[6], 16);
var seedAddr = new NativePointer(args[5]);
var seedBytes = new Uint8Array(Memory.readByteArray(seedAddr, seedLength));
var clientRandom = "";
var serverRandom = "";
if(seedLength == 64) {
for(i = 0; i < 32; i++) {
clientRandom += byteToHex(seedBytes[i]);
}
for( ; i < 64; i++) {
serverRandom += byteToHex(seedBytes[i]);
}
}
else if(seedLength == 77) { // key expansion
var offset = 13;
for(i = offset; i < 32 + offset; i++) {
serverRandom += byteToHex(seedBytes[i]);
}
for( ; i < 64 + offset; i++) {
clientRandom += byteToHex(seedBytes[i]);
}
}
Extract client and
server randoms
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if(clientRandom !== "") {
send("CLIENT_RANDOM "+ clientRandom + " " + secret);
}
}
}
});
Send it to the host
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DEMO
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Areas that need more work
★ TLS Session Resumption
★ Safari
★ iOS 11
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So what did I learn?
★ Just like on the web… sometimes we forget to
Compress JSON responses
Reuse connections
Optimise images
And a whole bunch of other things
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https://www.flickr.com/photos/willypayne/3116394973
Thank You
&
Happy Christmas!