Directory Traversal Affecting @backstage/techdocs-common package, versions <0.6.3
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-BACKSTAGETECHDOCSCOMMON-1300041
- published4 Jun 2021
- disclosed4 Jun 2021
- creditPatrik Oldsberg
Introduced: 4 Jun 2021
CVE-2021-32662 (opens in a new tab)How to fix?
Upgrade @backstage/techdocs-common to version 0.6.3 or higher.
Overview
@backstage/techdocs-common is a Common functionalities for TechDocs, to be shared between techdocs-backend plugin and techdocs-cli
Affected versions of this package are vulnerable to Directory Traversal. A malicious actor could read sensitive files from the environment where TechDocs documentation is built and published by setting a particular path for docs_dir in mkdocs.yml. These files would then be available over the TechDocs backend API. The attacker would need access to modify the mkdocs.yml in the documentation source code, and would also need access to the TechDocs backend API.
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