CVE-2020-28328 SuiteCRM RCE

Remediation testing

I found another vulnerability during remediation testing, and that writeup can be found here.

I recently discovered two vulnerabilities in SuiteCRM that provides an attack chain for a low privileged user to achieve code execution on the underlying operating system. The attack chain is Cross-Site Scripting, which can be used to perform Cross-Site Request Forgery, which leads to Remote Code Execution by tampering with the application configuration and poisioning a log file. This is all achieved via a file upload that contains malicious JavaScript that a low privileged user can trick a user with administrative privileges into running. The Proof-Of-Concept files and video I have attached demonstrates a low privileged user performing this attack and obtaining areverse shell on the system that is hosting SuiteCRM.
This was patched in version 7.11.17 of SuiteCRM.

Severity

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
I don’t fully agree with this rating as the exploit does require administrative access which would change PR:L to PR:H, adjusting the final score from an 8.8 to a 7.2.
I would rate it as: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Ref: https://nvd.nist.gov/vuln/detail/CVE-2020-28328

Version details

SuiteCRM Version 7.11.15

Cross-Site Scripting (XSS)

The stored Cross-Site Scripting exists in the ‘Create Documents’ file upload. A low privileged user is able to upload a file with any contents. The user can then examine the link provided to download this document and ascertain the file’s location on the filesystem by locating the id parameter. This long, random value is the name of the fileinside the /uploads/ directory. The user can place arbitrary JavaScript in this file and then send the link to another user. This can be used to hijack another user’s session and/or perform actions on that user’s behalf, which will be shown in the PoC video.

Remote Code Execution

After discovering that I could become the admin through session hijacking via the Cross-Site Scripting, I then discovered that I could control the system properties under ‘Admin → System Settings’, namely the log file property. Log file extensions were pretty well blocked, but I was able to use BurpSuite to update the ‘Log File Name’ value to be any arbitrary value, including .php extensions. I did this by submitting a request without changing anything and capturing the POST request that actually updates the values. I changed the filename via the logger_file_name parameter to shell.php and simply made the ‘Extension’ field blank. That provided a php file that I could access in browser at the webroot, but I needed some php code insidethe file to execute.
Next, I examined the output in the file and noticed that I could control input into the file via user properties if I updated a user (such as the user’s first or last name), if the logging was set to info (which I believe was default…). So, I captured a request in burp and inserted some php code <?php $id =`id`; echo $id; ?> in the last_name form field. This resulted in the output of the id command on Linux in the context of the web server user, www-data. The only characters that I could tell were escaped based on the log file are single quotes, double quotes, and back slashes. You can verify this by tail‘ing the sql log file on the backend.

Chaining the two for Cross-Site Request Forgery (One click -> shell)

I was able to perform all this as the admin user because I was able to obtain session cookies, however to have a working chain, I needed to have this execute via JavaScript in the context of the admin user. I was able to script this using a few fetch requests to perform each of these POST requests. The first one updated the system properties, the second updated the admin user’s ‘Last Name’ field, and the last performed a GET request on the newly created log file with malicious php code. The malicious php code would perform a curl request against my machine, pull down a bash reverse shell, and then pipe the output of that curl request directly to bash, executing the code. I then uploaded this using the same method that I discussed in the XSS section and revisited the new link as the admin user. With a web server hosting my bash file and a netcat listener running, I was able to get a reverse shell.

Mitigation

Cross-Site Scripting

Ensure you have AllowOveride All set in Apache. nginx does not have this setting and I did not test it on nginx.

Remote Code Execution

Update to the latest release of SuiteCRM, or at least version 7.11.17.
This is the specific fix. Commit 1618af16eaa494c4551bac961e5ac8fc3d87ab8c

Reporting to SuiteCRM

SuiteCRM was very responsive throughout the reporting process. They acknowledged the RCE, which was patched. The XSS was the result of a web server configuration so they did not acknowlede it as a vulnerability. They did, however, note that they would be updating the documentation in light of this.

Timeline

06 AUG 2020 -> Both issues reported to security@suitecrm.com
07 AUG 2020 <- SuiteCRM confirms receipt of report and raises issue with internal security team
21 AUG 2020 -> I contacted security@suitecrm.com for a follow up
25 AUG 2020 <- SuiteCRM replies regarding web server config/XSS
26 AUG 2020 -> I reply to say that the suggestion of AllowOveride All mitigates XSS
16 SEP 2020 -> I contacted security@suitecrm.com for a follow up
17 SEP 2020 <- SuiteCRM replies to confirm the issue as a partial issue
29 OCT 2020 Update released
03 NOV 2020 -> I contact security@suitecrm.com to ensure nothing else is needed on their end before releasing writeup
05 NOV 2020 <- SuiteCRM replies

Now we have released a patch for this issue and it is in the pubic domain, there is no problem with you doing a blog post on the vulnerabilities from our perspective.

05 NOV 2020 -> CVE requested by me
06 NOV 2020 <- CVE-2020-28328 issued

POC

https://www.exploit-db.com/exploits/49001

Thanks to SuiteCRM!

They were very easy to work with and I definitely plan to continue searching for and reporting vulnerabilities in this software!

• 2021 2
• 2020 4