The core Upload module in Drupal 4.7.x before 4.7.8 and 5.x before 5.3 places the .html extension on a whitelist, which allows remote attackers to conduct cross-site scripting (XSS) attacks by uploading .html files.
The hook_comments API in Drupal 4.7.x before 4.7.8 and 5.x before 5.3 does not pass publication status, which might allow attackers to bypass access restrictions and trigger e-mail with unpublished comments from some modules, as demonstrated by (1) Organic groups and (2) Subscriptions.
Drupal 5.2 and earlier does not properly unset variables when the input data includes a numeric parameter with a value matching an alphanumeric parameter's hash value, which allows remote attackers to execute arbitrary PHP code by invoking the drupal_eval function through a callback parameter to the default URI, as demonstrated by the _menu[callbacks][1][callback] parameter. NOTE: it could be argued that this vulnerability is due to a bug in the unset PHP command (CVE-2006-3017) and the proper fix should be in PHP; if so, then this should not be treated as a vulnerability in Drupal.