LocalTapiola: High server resource usage on captcha (viestinta.lahitapiola.fi)

ID H1:204208
Type hackerone
Reporter irotem2
Modified 2017-03-18T12:37:34


Basic report information

Summary: It is possible to generate a simple request which creates a high cpu/bandwidth consumption from the server by abusing the captcha servlet

Description: By sending a specially crafted request and changing the height/width parameters in the captcha form it is possible to consume large amount of cpu/memory and bandwidth.

By Sending a width 21800 and height 4800 the server responded after a few seconds with a payload of 318k. When increasing the height to 48000, the server responded after about 15 seconds with a payload of 3M.

Testing was stopped in order to prevent a full denial of service on the website but it seems that there is no limit and easily with a couple of requests we can deny service to the servlet and maybe even the whole server.

Domain: http://viestinta.lahitapiola.fi/

Browsers / Apps Verified In:

  • Chrome / CURL

Steps To Reproduce:

(Add details for how we can reproduce the issue)

  1. Send a request to the following url - http://viestinta.lahitapiola.fi/nms/jsp/captcha.jsp?captchaID=@vq-ooKP6OECsEZDMwxvQGKYlOO5cUAx8hD9Z856vdHI=,122&width=21800&height=4800&minWordSize=8&maxWordSize=8
  2. Increase the parameters width and height until server gets unresponsive or under heavy load


In the scope of testing I saw that denial of service is out of scope, This attack is more applicative and doesn't use distributed denial of service methods and I think it is important for you to fix this although it is not in scope