The following guide includes some security best practices that you should consider when developing a Cordova application. Please be aware that security is a very complicated topic and therefore this guide is not exhaustive. If you believe you can contribute to this guide, please feel free to file an issue in Cordova's bug tracker under "Documentation". This guide is designed to be applicable to general Cordova development (all platforms) but special platform-specific considerations will be noted.
Read and understand the Whitelist Guide
Domain whitelisting does not work on Android API 10 and below, and WP8 for iframes and XMLHttpRequest. This means an attacker can load any domain in an iframe and any script on that page within the iframe can directly access Cordova JavaScript objects and the corresponding native Java objects. You should take this into consideration when building applications for these platforms. In practice this means making sure you target an Android API higher than 10, and that if possible you do not use an iframe to load external content - use the inAppBrowser plugin or other third-party plugins.
If content is served in an iframe from a whitelisted domain, that domain will have access to the native Cordova bridge. This means that if you whitelist a third-party advertising network and serve those ads through an iframe, it is possible that a malicious ad will be able to break out of the iframe and perform malicious actions. Because of this, you should generally not use iframes unless you control the server that hosts the iframe content. Also note that there are third party plugins available to support advertising networks. Note that this statement is not true for iOS, which intercepts everything including iframe connections.
Cordova does not support true certificate pinning. The main barrier to this is a lack of native APIs in Android for intercepting SSL connections to perform the check of the server's certificate. (Although it is possible to do certificate pinning on Android in Java using JSSE, the webview on Android is written in C++, and server connections are handled for you by the webview, so it is not possible to use Java and JSSE there.) Since Apache Cordova is meant to offer consistent APIs across multiple platforms, not having a capability in a major platform breaks that consistency.
There are ways to approximate certificate pinning, such as checking the server's public key (fingerprint) is the expected value when your application starts or at other various times during your application's lifetime. There are third-party plugins available for Cordova that can do that. However, this is not the same as true certificate pinning which automatically verifies the expected value on every connection to the server.
There are also plugins that can do true certificate pinning for some platforms, assuming your app is able to do all of its network requests using the plugin (i.e.: no traditional XHR/AJAX requests, etc).
Using self-signed certificates on your server is not recommended. If you desire SSL, then it is highly recommended that your server have a certificate that has been properly signed by a well-known CA (certificate authority). The inability to do true certificate pinning makes this important.
The reason is that accepting self-signed certificates bypasses the certificate chain validation, which allows any server certificate to be considered valid by the device. This opens up the communication to man-in-the-middle attacks. It becomes very easy for a hacker to not only intercept and read all communication between the device and the server, but also to modify the communication. The device will never know this is happening because it doesn't verify that the server's certificate is signed by a trusted CA. The device has no proof that the server is who it expects. Because of the ease of doing a man-in-the-middle attack, accepting self-signed certificates is only marginally better than just running http instead of https on an untrusted network. Yes, the traffic would be encrypted, but it could be encrypted with the key from a man-in-the-middle, so the man-in-the-middle can access everything, so encryption is useless except to passive observers. Users trust SSL to be secure, and this would be deliberately making it insecure, so the SSL use becomes misleading. If this will be used on a trusted network (i.e., you are entirely inside a controlled enterprise), then self-signed certs are still not recommended. The two recommendations in a trusted network are to just use http because the network itself is trusted, or to get a certificate signed by a trusted CA (not self-signed). Either the network is trusted or it is not.
The principles described here are not specific to Apache Cordova, they apply to all client-server communication.
When running Cordova on Android, using android:debuggable="true" in the application manifest will permit SSL errors such as certificate chain validation errors on self-signed certs. So you can use self-signed certs in this configuration, but this is not a configuration that should be used when your application is in production. It is meant to be used only during application development.
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https://cordova.apache.org/docs/en/8.x/guide/appdev/security/index.html