Broken Access Control in Platinum Mobile

Title

Broken access control

Product

Platinum Mobile

Vulnerable Version

1.0.4.850

Fixed Version

1.0.4.851

CVE Number

-

Impact

critical

Found

04.24.2020

By

Mingshuo Li (Office Munich) | SEC Consult Vulnerability Lab

The identified authorization bypass vulnerability allows an authenticated attacker to access confidential information of other users including payrolls.

Vendor Description

“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.”

Source: https://www.platinumchina.com/en/products/p11

Business Recommendation

It is recommended to apply the hotfix or update the server component to version 1.0.4.851.

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:

  • 1.0.4.864 on Android
  • 1.0.4.864 on iOS
  • 1.0.4.850 on Server

Vendor Contact Timeline

2020-05-19 Contact vendor through the provided email address.
2020-05-20 Exchange on the issue.
2020-05-22 Vendor acknowledged the issue, and claimed a hotfix will be released before a fix in the next version.
2020-07-22 Contact the vendor again.
2020-07-23 Vendor informed that a hotfix has been released.
2020-08-19 Customer confirmed that the hotfix works.
2020-10-01 Release of the advisory.

Solution

Apply the hotfix or update the application to the latest version 1.0.4.851.

Workaround

None.

Advisory URL

Vulnerability Lab

 

EOF Mingshuo Li / @2020

 

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