K-Gen has discovered a vulnerability in phpBB, which can be exploited by malicious people to conduct script insertion attacks.
The vulnerability is caused due to an input validation error in the avatar upload handling. This can exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected site by uploading a specially crafted valid image containing embedded HTML and script code with an image file extension not matching the image type (e.g. a valid GIF file with a ".jpg" file extension).
This may be related to vulnerability #2 in: SA15845
Successful exploitation requires that the malicious avatar is accessed directly in the Microsoft Internet Explorer browser (i.e. not referenced via an image tag) and that the "avatar uploading" setting is enabled (not default setting).
The vulnerability has been confirmed in version 2.0.17. Other versions may also be affected.
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