CVE-2023-27534: Path Traversal Vulnerability in curl's SFTP Implementation

A recently discovered security vulnerability, identified as CVE-2023-27534, exists in the widely used data transfer tool, curl. This vulnerability allows attackers to perform path traversal attacks using the SFTP protocol in curl prior to version 8... Users must update their curl installation to the latest version immediately to protect themselves from potential attacks. In this post, we will dive deep into the details of this vulnerability, provide examples of the malicious code, and discuss how to mitigate the risk.

The Vulnerability

The path traversal vulnerability lies in curl's SFTP implementation, where the tilde (~) character is mistakenly replaced when used as a prefix in the first path element. The tilde character is intended to represent the user's home directory when used as the first element of a path. However, in versions prior to 8.., this character is replaced even if it's not the first element in the path.

Exploit Details

Attackers can exploit this flaw by crafting a malicious path, such as /~2/foo, while accessing a server with a specific user. The attacker can then bypass filtering or execute arbitrary code on the system. To demonstrate this vulnerability, we will show an example of a code snippet using curl's command line tool:

$ curl -u username:password sftp://localhost/~/path/to/vulnerable/file

By using the crafted path mentioned earlier, the attacker can exploit the vulnerability

$ curl -u username:password sftp://localhost/~2/foo

This code snippet accesses the targeted server using the SFTP protocol with a provided username and password, and the crafted path bypasses any filters and potentially allows arbitrary code execution.

Original References

The curl project has published the details of this vulnerability in a security advisory, along with the mitigation steps and the updated version of curl that contains the fix. You can read more about this issue and its mitigation on the project's official website:

- curl Security Advisory
- curl Releases - Fixed in Version 8..

Mitigation

The curl project has fixed this vulnerability in version 8... Users must update their curl installations to this version or later as soon as possible to protect themselves from potential attacks exploiting this vulnerability. To update your curl installation, follow these steps:

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Replace apt-get with the appropriate package manager for your Linux distribution (e.g., yum, zypper, or pacman).

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3. On Windows systems, download the latest version of curl from the official website and follow the installation instructions:

  - curl for Windows

Final Thoughts

The path traversal vulnerability in curl's SFTP implementation, identified as CVE-2023-27534, is a critical security issue that requires immediate attention. Users must update their curl installations to version 8.. or later to mitigate the risk of attackers bypassing filters or executing arbitrary code on their systems. Stay vigilant about updating software packages to protect yourself from potential cybersecurity threats in the future.

Timeline

Published on: 03/30/2023 20:15:00 UTC
Last modified on: 04/20/2023 09:15:00 UTC