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[iOS] - Fix securing message handlers on iOS-18 #26014

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merged 2 commits into from
Oct 17, 2024
+22 −11
Merged

[iOS] - Fix securing message handlers on iOS-18 #26014

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71d7d48
Fix securing message handlers on iOS 18.
Brandon-T Oct 15, 2024
9b853e7
SetInterval and SetTimeout can be exploited with a race condition. Ch…
Brandon-T Oct 16, 2024
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30 changes: 19 additions & 11 deletions ios/brave-ios/Sources/Brave/Frontend/UserContent/UserScripts/__firefox__.js
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Original file line number Diff line number Diff line change
Expand Up @@ -131,11 +131,9 @@ if (!window.__firefox__) {
let $Function = secureCopy(Function);
let $Reflect = secureCopy(Reflect);
let $Array = secureCopy(Array);
let $webkit = window.webkit;
let $MessageHandlers = $webkit.messageHandlers;

secureCopy = undefined;
let secureObjects = [$Object, $Function, $Reflect, $Array, $MessageHandlers];
let secureObjects = [$Object, $Function, $Reflect, $Array];

/*
* Prevent recursive calls if a page overrides these.
Expand Down Expand Up @@ -412,14 +410,24 @@ if (!window.__firefox__) {
return Promise.reject(new TypeError("undefined is not an object (evaluating 'webkit.messageHandlers')"));
}

let webkit = window.webkit;
delete window.webkit.messageHandlers[messageHandlerName].postMessage;
delete window.webkit.messageHandlers[messageHandlerName];
delete window.webkit.messageHandlers;
delete window.webkit;
let result = $MessageHandlers[messageHandlerName].postMessage(message);
window.webkit = webkit;
return result;
return new Promise((resolve, reject) => {
var oldWebkit = window.webkit;
delete window['webkit'];

// WebKit no longer restores the handler immediately! So we poll for when that happens and resolve the promise accordingly.
const timeout = 5000;
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@stoletheminerals stoletheminerals Oct 16, 2024 •
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A few concerns I have.

  1. Does it wait 5 seconds before trying to postMessage? Isn't it a lot for some use cases?
  2. Also a web page can race during this time out and modify window.webkit once it is restored (or before it is restored, I'm not sure what happens in this case)

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@Brandon-T Brandon-T Oct 16, 2024 •
edited
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  1. Fixed.
  2. Fixed.

I tested with:

let interval = setInterval(function() {
  console.log("Replace window.webkit with hacked version");
}, 0);

setTimeout(function() {
   let startTime = Date.now();
    while(true) {
        console.log("Polling for window.webkit legit version");
        if (Date.now() - startTime >= 5000) {
          clearInterval(interval);
          break;
        }
    }
}, 0);

To see if the loop will block the setInterval. So even if a page tries to replace the window.webkit inside of setInterval or something similar, the while loop is synchronous and it blocks ALL other operations (async included).

Only once the while loop completes, everything else executes :) so I changed the code to use a while loop with a timeout. I checked performance and there's no issue as webkit replaces it internally asynchronously, in the next execution frame, while the loop blocks the page from executing anything else.

let startTime = Date.now();
var timerId = setTimeout(() => {
if (window.webkit.messageHandlers && window.webkit.messageHandlers[messageHandlerName]) {
let result = window.webkit.messageHandlers[messageHandlerName].postMessage(message);
window.webkit = oldWebkit;
clearTimeout(timerId);
result.then(resolve).catch(reject);
} else if (Date.now() - startTime >= timeout) {
reject(new TypeError("undefined is not an object (evaluating 'webkit.messageHandlers')"));
}
}, timeout);
});
};

$.dispatchEvent = function(event) {
Expand Down
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