DNN (formerly DotNetNuke) is an open-source web content management platform (CMS) in the Microsoft ecosystem. The algorithm used to generate the captcha image shows the least complexity of the desired image. For this reason, the created image can be easily read by OCR tools, and the intruder can send automatic requests by building a robot and using this tool. This vulnerability is fixed in 9.13.8.
The product uses a CAPTCHA challenge, but the challenge can be guessed or automatically recognized by a non-human actor.
An automated attacker could bypass the intended protection of the CAPTCHA challenge and perform actions at a higher frequency than humanly possible, such as launching spam attacks. There can be several different causes of a guessable CAPTCHA: