Wednesday, 5 December 2012

Maxthon - Incorrect Executable File Handling and Same Origin Policy Implementation




Details

Vendor Site: Maxthon (www.maxthon.com)
Date: December, 5 2012 – CVE (TBA)
Affected Software: Maxthon 3.4.5.2000 and previous versions
Status: Patched
Researcher: Roberto Suggi Liverani - @malerisch
PDF version: Maxthon_multiple_vulnerabilities_advisory.pdf


Incorrect Executable File Handling


The way local executable files are handled by the Maxthon browser seems related to the fact that external tools such as Calc, Desktop, and others can be launched from the browser itself. This design is insecure as it allows JavaScript to directly invoke an executable. As shown in previous exploits, this design can aid exploitation by chaining different vulnerabilities at the same time, allowing for arbitrary command execution.

This vulnerability can be exploited in multiple ways:

Scenario 1
1. User visits a page which invokes the window.open() function against an executable file – e.g. file:///C:/windows/system32/cmd.exe
2. User unblocks the pop up blocker

Scenario 1 - Impact
The window will open as a new window, SOP is not enforced and this vulnerability would allow arbitrary code execution.

Scenario 2
User is fooled into bookmarking an executable file

Scenario 2 - Impact
Executable is executed directly by Maxthon. User is not prompted to either downloading the executable or discarding the download.

Scenario 3
SOP vulnerability discovered that would allow direct access to file:// zone from an untrusted zone

Scenario 3 - Impact
Arbitrary command execution.


Same Of Origin (SOP) Incorrect Implementation

It is possible to bypass Same of Origin of Policy  (SOP) by using window.open() method against about: URI scheme. Such URI are mapped to privileged zone mx://res/*. However, by invoking directly against mx://res/, the SOP is applied and access is forbidden. The following table summarises test case conducted with window.open() method:
  1. http:// -> file:// - Prompts a popup blocker, if the user allows the pop up, the file:// window is opened.
  2. http:// -> about:* - Spawns a new window
  3. http:// -> mx://res/* - Forbidden by SOP
Timeline

13/02/2012 - Bug reported to multiple contacts
21/02/2012 - Reception of report confirmed but no further reply
21/02/2012 - Chased vendors - no reply
12/05/2012 - HITB2012AMS - bug disclosed during presentation
02/11/2012 - 25 new releases following the report – 2 bugs silently fixed
14/11/2012 - HackPra - bug and exploit module presented

Solution

Do not use Maxthon browser.

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