The activation resend function in the Profiles module in XOOPS before 2.4.1 sends activation codes in response to arbitrary activation requests, which allows remote attackers to bypass administrative approval via a request involving activate.php.

userinfo.php in XOOPS 1.0 RC1 allows remote attackers to obtain sensitive information via a SQL injection attack in the "uid" parameter.

Cross-site scripting (CSS) vulnerabilities in the Private Message System for XOOPS 1.0 RC1 allow remote attackers to execute Javascript on other web clients via (1) the Title field or a Private Message Box or (2) the image field parameter in pmlite.php.

The custom avatar uploading feature (uploader.php) for XOOPS 2.0.9.2 and earlier allows remote attackers to upload arbitrary PHP scripts, whose file extensions are not filtered.