Develop Reference

Some androids apps won't connect through fiddler

I have followed instructions on how to add fiddler certificate on android emulator, using both nox and memu emulators, as well as my android phone running marshmallow, I set the WiFi proxy to point to my PC over the local network, when I open a website using a web browser, things work fine, I receive the warning, I choose to proceed and the connection is successfully tunneled and decrypted using fiddler.
But, when I try to use other apps, connections fail! I see the tunnel connections, and then connection fails. My bet is, it's due to the invalid HTTPS certificate, so my question is, is there a way for me to install fiddler to the trusted authorities so connecting to it will go through without the warning? So I can finally debug HTTPS traffic from and to those apps.
I found similar questions here on SO, but none of them were exactly the same as mine, nor did they have the right answers, so I'm not sure if this question does in fact qualify as a duplicate.
Thanks

On modern Android devices using apps developed for target API Level 24 (Android 7) or higher sniffing traffic is not that simple anymore. The target API level of an app is defined it's AndroidManifest.xml file in the entry <uses-sdk android:targetSdkVersion="??"/>.
The main problem is that if you install the Fiddler root CA certificate in Android it is marked as user certificate (not system certificate). And unless explicitly configured in an app those user certificates are not trusted.
One of those rare apps that respect user CA certificates is Chrome. So using Chrome for testing if the proxy and the installed root CA certificate works is a bad idea, as it may only work in Chrome but not for apps.
Note that some apps further use certificate pinning (leaf or root CA pinning). Therefore even if the Fiddler root CA certificate is installed as system certificate the app won't trust this certificate as it fails on the certificate pinning.
Certificate pinning is also a web site feature, hence some sites save a certificate hash in the web browser cache that pins the site to a certain certificate. In such a case clearing the browser cache is usually removing those pinning data.
Rooted devices
If your device is rooted you can try to install the Fiddler root CA certificate as system certificate. The Mitmproxy documentation contains a how-to for manually installing the mitmproxy certificate.
If you have rooted the phone using Magisk, there is a Magisk module that seems to be able to install user certificates automatically as system certificates: https://github.com/NVISO-BE/MagiskTrustUserCerts
Alternatively you can install Magisk + Edxposed + TrustMeAlready Xposed module. This allows to disable certificate checking system wide - WARNING: this eliminates the security of SSL/TLS against active attacks, for all apps on the phone. Therefore only do this on a device you use just for hacking!
Also possible is installing and run Frida-Server on the device and hook into the app you are interested to modify the SSL/TLS certificate checking at run-time. AFAIK the Frida based framework Objection has some scripts to do so.
Non-rooted device
On a non-rooted device there is only the option to modify the application before you install it onto the device. Note that some apps will detect that they have been modified and will refuse to work.
To let the app trust user certificates you have to modify network_security_config.xml (see e.g. here) included in the app. You can use apktool to decompile/recompile the app. Don't forget to re-sign the recompiled/repackaged app e.g. using apksigner from Android SDK.
There are some tools available that automate the decompiling , modification and signing like apk-mitm.
There is also the possibility to modify an app by including the Frida gadget for Android into the app. This would allow to use Frida for this specific app on a non-rooted device.

Use mkcert certificate for local testing of PWA

I'm trying to setup a local dev environment for a PWA I'm working on.
I have installed mkcert on my Mac and am able to host a https://localhost version on my computer.
Now I'd like to open the page on my Android phone. On the mkcert github it says:
Mobile devices
For the certificates to be trusted on mobile devices,
you will have to install the root CA. It's the rootCA.pem file in the
folder printed by mkcert -CAROOT.
On iOS, you can either use AirDrop, email the CA to yourself, or serve
it from an HTTP server. After installing it, you must enable full
trust in it. Note: earlier versions of mkcert ran into an iOS bug, if
you can't see the root in "Certificate Trust Settings" you might have
to update mkcert and regenerate the root.
For Android, you will have to install the CA and then enable user
roots in the development build of your app. See this StackOverflow
answer.
https://github.com/FiloSottile/mkcert
I installed the rootCA.pem on my phone. The part about "enabling user roots" doesn't apply, since this is not an app.
But when I open the page on my phone using https://[my-local-network-ip]:1234 I get a warning, that the certificate can't be trusted.
How can I trust the certificate so I can locally test the PWA on my phone?

I know you've probably moved on from this question, as it's almost a year on. However, I would like to share how I was able to test my PWA locally in a secure context.
Not making any assumptions about what framework / packaging / build system you're using:
Generate a certificate & key using mkcert. If you are hosting your PWA locally & want to access it over your local IP address i.e. 192.168.1.x:3000 you also need to tell mkcert to generate a certificate that covers that IP address:
mkcert localhost 192.168.1.17
// The certificate is at "./localhost+1.pem" and the key at "./localhost+1-key.pem" ✅
Important note: most routers dynamically assign local IP addresses, so it's worthwhile assigning a static IP.
Install your RootCA from mkcert onto your iOS or Android device. Follow the instructions in the mkcert docs
Serve your generated certificates with your web server of choice. I use Create React App. You can see my answer about PWAs in secure context here

I agree with your goal - running a local TLS based setup can be useful in terms of productivity and early troubleshooting.
Your problem is DNS based and you need to access the TLS secured URL via the host name.
The only way you'll get DNS to match up on the Android side is to use an HTTP proxy, while running either an emulator or a device connected via USB.
In a nutshell I would do this:
Issue your cert to a more real world domain name such as mycompany.com
Add this domain name to DNS on your Mac book
Install a free proxy such as proxyman on the Mac
Configure the Android emulator or device to use the proxy (you will also need to trust the proxy's cert on Android and the Mac)
Then browse to https://mycompany.com from Android
Full details are available in my write up

How to fix broken HTTPS on android when using a openssl self signed localhost certificate?

I followed this guide on how to create my own CA and end entity certificates. My certificate authority (localhost) openssl config looks very similiar to this. According to this post I've set
[ v3_ca ]
basicConstraints = CA:TRUE
On my desktop devices there are no problems at all and https works fine.
Problems occur when I try to install the root certificate on my android device.
At first I installed the root certificate via the inbuilt 'install from storage' option (Settings / Security / Credential storage). Https works now but I always get the network may be monitored warning.
Following this article I took the certificate hash, renamed the rootca.pem file to {hashid}.0 file as suggested and moved it to /system/etc/security/cacerts/ using ADB on windows powershell (also set chmod and chown).
After rebooting my phone I can see that my authority certificate has been successfully added to android native trusted certificate storage. It's active by default.
Now I got rid of the networking monitor warning but ssl is not working anymore. Android chrome on remote debug throws:
broken https certificate missing net::ERR_UNEXPECTED (firefox on android says SEC_ERROR_UNKNOWN_ISSUER)
Is there a way to get around this/install it correctly? Did I forget something?

For those interested I'm sharing the solution:
Here's what I did to solve this:
(1) flashing my sm-g900f with odin v3.12.4-4 and latest twrp 3.3.0-0-klte
(2) backup relevant data, wipe system/cache/... with twrp afterwards
(3) flash 16.0-nightly-klte addonsu-16.0-arm open_gapps-arm-9.0-nano-20190428
(4) install certificate via security settings options. Shown as 'user cert' but no warning message and ssl works now :)
Thanks to JW09I4 from XDA-Developers for helping me out and guiding me through the process of updating my phone.

Charles proxy fails on SSL Connect Method

I have Android 4.3 forced to use Charles proxy via IPTABLES.
The charles certificate is installed on the phone.
I am able to capture normal SSL traffic like https websites in the browser.
All POST and GET methods seem to work fine.
In a particular app, it fails when using the SSL CONNECT method.
URL: https://XX.XX.XXX.XXX/
Status: Failed
Failure: SSLHandshake: Received fatal alert: unknown_ca
Response Code: - Protocol: HTTP/1.0
Method: CONNECT

From iOS 10.3 you also need to go to Settings > General > About > Certificate Trust Settings and trust Charles certificate.

You can face with this problem at some applications like Facebook or Instagram.
Charles certificate doesn't work at some new apps because they are using a technique named as SSL-PINNING. First of all you have to break ssl-pinning system of application or you can instal old version of application then it sometimes works but we need a new solution about ssl pinning in order to record traffic for this kind of applications.

as #Berkay Yıldız says, it probably using ssl/certificate pinning.
how to fix/avoid/disable ssl pinning?
the whole logic is:
LEVEL 1: for normal http：
core logic：
PC：Mac/Windows
Charles set http proxy
set port
app use Charles proxy
inside Wifi, set
host IP
port
Note：
computer side, MUST use wired network, NOT wireless, otherwise mobile side network not usable
LEVEL 2: for encrypted https：
PC
install Charles root certificate
Mac：use Key Chain to trust Charles Root CA
Charles
Enable SSL Proxying
set location filter for your specific api address
phone
app
install Charles Root CA
Note: type should select: VPN and Application
NOT select：WLAN
makesure certificate install successfully
Trusted Credentials -> User, can see installed Charles certificate
LEVEL 3: for SPECIAL https which using ssl pinning:
Phone：
make sure root or jailbreak
Android：has rooted
for later to install tool: Xposed
iOS：has jail break
for later to install tool: Cydia
then install plugin/tool, capable of avoid/disable ssl pinning
Android：
JustTrustMe (based on Xposed)
Android-SSL-TrustKiller (Cydia Substrate)
iOS：
SSL Kill Switch 2 (based on Cydia)
old version：iOS SSL Kill Switch (based on Cydia)
more detailed summary please refer my post (written in Chinese): 1 and 2

Some folks my end up here with android N Devices that won't do SSL over charles even after installing the cert - now on http://chls.pro/ssl
In N - you need to also add an xml file and security config. This post goes into more details: How to get charles proxy work with Android 7 nougat?

I have met the same problem. And after installing the latest certificate, it is solved.

On your phone, visit http://charlesproxy.com/getssl to download the cert. Upon downloading the cert in android, it will prompt you to install the cert, give the cert a name and continue. It should now work.
Note: The sshould be similar on an iPhone

I got the following error when I was trying to install the cert on my Nexus 6p, Android 6.0. (I followed the instructions in charles and downloaded the cert via http://chls.pro/ssl.):
Couldn't install because the certificate file couldn't be read.
The solution to this problem was to install via:
Settings > Security > Install from storage
After navigating to the cert file and installing it everything worked as expected.

On this link http://www.charlesproxy.com/documentation/using-charles/ssl-certificates/ you have all the information you need on properly installing the Charles certificate.
After installing it you'll get rid of the "SSLHandshake: Received fatal alert: unknown_ca" error.

If you get this with an app using facebook login on an android phone, I got around it by uninstalling the fb app. Then the mobile fb web is used instead and I can charles everything. With the fb app installed the fb api fails with SSL error.

On Samsung phones, you should install the certificate by navigating to Biometrics and security/Other security settings/Install from device storage/CA Certificate.

I am using Charles 4.2.5 and Nexus 6P on Android 8.1.
One cannot use Charles to track https on my mobile phone.
Plz note that after Android N, we cannot capture normal SSL traffic of others'app.
Here is the official website of Charles.
https://www.charlesproxy.com/documentation/using-charles/ssl-certificates/
Android As of Android N, you need to add configuration to your app in
order to have it trust the SSL certificates generated by Charles SSL
Proxying. This means that you can only use SSL Proxying with apps that
you control.
In order to configure your app to trust Charles, you need to add a
Network Security Configuration File to your app. This file can
override the system default, enabling your app to trust user installed
CA certificates (e.g. the Charles Root Certificate). You can specify
that this only applies in debug builds of your application, so that
production builds use the default trust profile.
Add a file res/xml/network_security_config.xml to your app:
Then add a reference to this file in your app's manifest, as follows:
...

Android Emulator appears not to trust Security Certificates in Browser

So I am running a few automated tests on an android emulator. I have two environments, my development PC running the android emulator, and our testing server running the android emulator. When I open the emulator and the browser app within the emulator, I can navigate to secure websites no problem. (For instance, google mail). However, in my testing server environment, I am seeing certificate errors on sites whose certificates should well be trusted. Is there an emulator configuration option for certificates that I am missing? Does the emulator need to connect to a service to verify the certificates and does not have access?

Ensure that the date and time are set properly on the emulator. An incorrect time setting may well invalidate the certificate because it's not within validity window.