YaBB Arbitrary File Read Vulnerability
YaBB.pl, a web-based bulletin board script, stores board postings in numbered text files. The numbered file name is specified in the call to YaBB.pl in the variable num=<file>. Before retrieving the file, YaBB will append a .txt extension to <file>.
Due to input validation problems in YaBB, relative paths can be specified in <file>. This includes ../ style paths.
Additionally, <file> does not need to be numerical, and the .txt extension can be avoided by appending %00 to <file>.
By exploiting these problems in a single request, a malicious user can view any file that the webserver has access to.