A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.
Example: The following C# code accepts an HTTP request and stores the usrname parameter in the HTTP session object before checking to ensure that the user has been authenticated.

usrname = request.Item("usrname");
if (session.Item(ATTR_USR) == null) {
    session.Add(ATTR_USR, usrname);
}

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following code passes an untrusted item (URL) from an iOS extension JavaScript script to the iOS Extension code.

    var GetURL = function() {};
    GetURL.prototype = {
        run: function(arguments) {
            ...
            arguments.completionFunction({ "URL": document.location.href });
        }
        ...
    };
    var ExtensionPreprocessingJS = new GetURL;
    

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following Kotlin code accepts an HTTP request and stores the usrname parameter in the HTTP session object before checking to ensure that the user has been authenticated.

val usrname: String = request.getParameter("usrname")
if (session.getAttribute(ATTR_USR) != null) {
    session.setAttribute(ATTR_USR, usrname)
}

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as a line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following code passes an untrusted item from an iOS extension to the host webview.

#import <MobileCoreServices/MobileCoreServices.h>

- (IBAction)done {
    ...
    [self.extensionContext completeRequestReturningItems:@[untrustedItem] completionHandler:nil];
}

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.
Example: The following code accepts a usrname cookie and stores its value in the HTTP DB session before it verifies that the user has been authenticated.

...
IF (OWA_COOKIE.get('usrname').num_vals != 0) THEN
usrname := OWA_COOKIE.get('usrname').vals(1);
END IF;
IF (v('ATTR_USR') IS null) THEN
HTMLDB_UTIL.set_session_state('ATTR_USR', usrname);
END IF;
...

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following Python code accepts an HTTP request and stores the username parameter in the HTTP session object before checking to ensure that the user has been authenticated.

uname = request.GET['username']
request.session['username'] = uname

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as a line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following code passes an untrusted item from an iOS extension to the host webview.

import MobileCoreServices

@IBAction func done() {
    ...
    self.extensionContext!.completeRequestReturningItems([unstrustedItem], completionHandler: nil)
}

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.

A trust boundary can be thought of as line drawn through a program. On one side of the line, data is untrusted. On the other side of the line, data is assumed to be trustworthy. The purpose of validation logic is to allow data to safely cross the trust boundary--to move from untrusted to trusted.

A trust boundary violation occurs when a program blurs the line between what is trusted and what is untrusted. The most common way to make this mistake is to allow trusted and untrusted data to commingle in the same data structure.

Example: The following code accepts an HTTP request and stores the usrname parameter in the HTTP session object before checking to ensure that the user has been authenticated.

...
Dim Response As Response
Dim Request As Request
Dim Session As Session
Dim Application As Application
Dim Server As Server
Dim usrname as Variant
Set Response = objContext("Response")
Set Request = objContext("Request")
Set Session = objContext("Session")
Set Application = objContext("Application")

usrname = Request.Form("usrname")
If IsNull(Session("ATTR_USR")) Then
	Session("ATTR_USR") = usrname
End If
...

Without well-established and maintained trust boundaries, programmers will inevitably lose track of which pieces of data have been validated and which have not. This confusion eventually allows some data to be used without first being validated.