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Epic Games Fortnite 4.2-CL-4072250 Insecure File Permissions

Medium
Advisory ID
ZSL-2018-5469
Release Date
21 May 2018
Vendor
Epic Games, Inc. - https://www.epicgames.com
Affected Version
4.2-CL-4072250, 4.1-CL-4053532, 4.0-CL-4039451
CVE
N/A
Tested On
Microsoft Windows 10 Home
Summary

Fortnite is a co-op sandbox survival game developed by Epic Games and People Can Fly and published by Epic Games. The game was released as a paid-for early access title for Microsoft Windows, macOS, PlayStation 4 and Xbox One on July 25, 2017, with a full free-to-play release expected in 2018. The retail versions of the game were published by Gearbox Publishing, while online distribution of the PC versions is handled by Epic's launcher.

Description

Fortnite suffers from an elevation of privileges vulnerability which can be used by a simple authenticated user that can change the executable file with a binary of choice. The vulnerability exist due to the improper permissions, with the 'C' flag (Change) for 'Authenticated Users' group.

Proof of Concept
Disclosure Timeline
10.04.2018Vulnerability discovered.
09.05.2018Vendor contacted.
11.05.2018Vendor replied confirming message received.
20.05.2018No response from the vendor.
21.05.2018Public security advisory released.
Credits
Vulnerability discovered by Gjoko Krstic
References
Changelog
21.05.2018Initial release
29.05.2018Added reference [1], [2] and [3]