[SA18544] MyBB "Allow HTML in Signatures" Script Insertion Security Issue

TITLE:
MyBB "Allow HTML in Signatures" Script Insertion Security Issue

SECUNIA ADVISORY ID:
SA18544

VERIFY ADVISORY:
http://secunia.com/advisories/18544/

CRITICAL:
Less critical

IMPACT:
Cross Site Scripting

WHERE:
>From remote

SOFTWARE:
MyBB (formerly MyBulletinBoard) 1.x
http://secunia.com/product/4479/

DESCRIPTION:
Night_Warrior has discovered a security issue in MyBB, which can be
exploited by malicious people to conduct script insertion attacks.

Input passed in a user's signature isn't properly sanitised before
being used. This can be exploited to inject arbitrary JavaScript
code, which will be executed in a user's browser session in context
of an affected site when the malicious signature is viewed.

Example:
<img
src=&#106&#97&#118&#97&#115&#99&#114&#105&#112&#116&#58[code (HTML
entities encoded)]>

Successful exploitation requires that "Allow HTML in Signatures" is
enabled (not default setting).

The security issue has been confirmed in version 1.02. Other versions
may also be affected.

SOLUTION:
Disable "Allow HTML in Signatures" in "User Registration and Profile
Options".

PROVIDED AND/OR DISCOVERED BY:
Night_Warrior

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