CVE-2023-4624: Critical Server-Side Request Forgery (SSRF) Vulnerability Discovered in BookStack App Before v23.08

A highly critical security vulnerability, CVE-2023-4624, has been discovered in the GitHub repository bookstackapp/bookstack versions prior to v23.08. The vulnerability is a Server-Side Request Forgery (SSRF), which could potentially allow attackers to initiate unauthorized requests from the vulnerable server to other internal or external systems.

This post will guide you through the details of this vulnerability, including the code snippets, a brief on the exploit, and links to the original references related to this issue.

Vulnerability Details

CVE-2023-4624 is a severe SSRF vulnerability that impacts the BookStack app before the v23.08 release. This vulnerability occurs due to the insecure handling of embedded content in the "Page Select" feature. The affected versions of BookStack do not properly validate user-supplied URLs for embedded content, allowing attackers to craft malicious URLs that could lead to SSRF attacks.

The following code snippet demonstrates the vulnerable code in the affected versions of BookStack

$page_slug = $request->get('page-slug');
$url = route('books.page.select.embed',$book->slug) . "?url=$page_slug";
$content = file_get_contents($url);

In the above code snippet, the $url variable is constructed without proper sanitization or validation of the user-supplied $page_slug, resulting in a potential SSRF vulnerability.

Exploit

An attacker could exploit this vulnerability by crafting a malicious URL containing an embedded link to a desired target server. When an unsuspecting user opens the crafted URL, the attacker can force the vulnerable server to initiate unauthorized requests to the target server. This could potentially lead to the compromise of sensitive information, security bypasses, or Denial of Service (DoS) on the affected systems.

For example, an attacker might create a URL resembling the following

http://<vulnerable_bookstack_server>/books/123/page-select?embed?url=http://<internal_or_external_server>/sensitive_endpoint

In this case, the attacker is targeting the internal or external server with the endpoint /sensitive_endpoint.

Mitigation

The developers of the BookStack app have addressed the vulnerability in the v23.08 release. Users are strongly advised to update their BookStack installations to the latest version (v23.08 or later) to protect themselves from potential SSRF attacks.

Link to Original References

To learn more about the CVE-2023-4624 vulnerability and the patches released by the developers, please refer to the following resources:

1. BookStack GitHub Repository: https://github.com/BookStackApp/BookStack
2. BookStack Changelog (v23.08): https://github.com/BookStackApp/BookStack/blob/master/CHANGELOG.md#v2308
3. CVE-2023-4624 Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4624

Conclusion

The CVE-2023-4624 SSRF vulnerability in the BookStack app is a serious security risk for affected users. It is essential to update your BookStack installation to the patched version (v23.08) to prevent the exploitation of this vulnerability. Stay informed about other similar vulnerabilities by following trusted resources and keeping your software up-to-date.

Timeline

Published on: 08/30/2023 13:15:00 UTC
Last modified on: 09/01/2023 19:59:00 UTC