“Platinum Mobile is a mobile office system based on Platinum HRM and ESS Workflow to realize HR informatization management, taking portable devices such as mobile phone, tablet pc as its main form and carrier. The new mobile solution will enable employees quickly and conveniently deal with affairs and not limited by time and place, thus effectively expedite the efficiency of internal communication and operations. Users can directly use their mobile devices landing on the client side to complete a series of tasks. Meanwhile, the executive have the access to making decisions and approvals anytime and anywhere.”
It is recommended to apply the hotfix or update the server component to version 126.96.36.1991.
Vulnerability Overview / Description
1) Broken access control
The mobile application connects to the company-specific server, which does not properly restrict the access to confidential data. Thus, an authenticated attacker can disclose the company’s payroll, personal information of other employees without having appropriate privileges to do so.
Proof Of Concept
1) Broken access control
The mobile application’s request consists primarily of two parts: an XML message in the body and its MD5 hash in the query string.
POST /MobileHandler.ashx?MessageHash=43a98be456b0213ce45e23fdf54c58b8 HTTP/1.1 Host: [redacted] Content-Length: 276 <Message ID="msg1" MessageType="InvokeServiceMessage" Service="Payslip" Method="getMyPayslipMonthInfoForReleaseMany" Language="English" UserCode="user0" TokenID=""> <Parameters><String>0000000537</String><DateTime>2020-03-31 00:00:00</DateTime><null/> </Parameters></Message>
Analyzing the mobile application reveals the following algorithm to calculate the hash:
MessageHash = hex_md5(escape(XmlMsg) + TokenID);
Furthermore, the server-side part of the application runs the following logic to verify the message:
- extract the “UserCode” value from the message
- look up the “TokenID” associated with the “UserCode”
- calculate and compare the hash
- if valid, trust and use the parameters in the message, which serves as the real reference (rather than the “UserCode”) to the business data.
Given this information, an authenticated attacker can craft a message with an arbitrary value set (e.g. 0000000537) for the element “Parameters” and calculate the hash with the attacker’s “UserCode” and “TokenID”.
As a consequence, the pay slip of another employee (e.g. a higher-ranked manager) can be disclosed. By iterating the values, the attacker can reveal the entire payroll data of the whole company.
In the following example an authenticated user “user0” can collect personal information of “user1”, including phone number, emails etc.
POST /platinummobile/Handlers/MobileHandler.ashx?MessageHash=bf62c16cad7a6b27b0fee8e1a21409b7 HTTP/1.1 Host: [redacted] Content-Length: 203 <Message ID="msg1" MessageType="InvokeServiceMessage" Service="MyAccount" Method="GetMyInfo" Language="English" UserCode="user0" TokenID=""> <Parameters><String>user1</String></Parameters></Message>
Vulnerable / Tested Versions
The following version has been tested, which was the most recent one at the time of the test:
- 188.8.131.524 on Android
- 184.108.40.2064 on iOS
- 220.127.116.110 on Server