There's a new vulnerability in town, and its name is CVE-2023-4696. This security issue affects the popular open-source project usememos/memos, versions prior to .13.2. The vulnerability stems from a flaw in access control, and it could potentially allow unauthorized users to gain access to sensitive information, or even execute malicious actions. In this long-read post, we'll take a deep dive into the details of this vulnerability, how to exploit it, and how to fix it. Before going into the details, let's understand the basics.

What is Access Control in GitHub?

Access control is a security measure used to restrict users from accessing specific resources or performing certain actions. On GitHub, access control can be implemented on repositories at the organization or individual level, with different levels of access granted to collaborators, such as read, write, or admin permissions.

A Simple Exploit for CVE-2023-4696

This vulnerability stems from improper access control, which may allow attackers to bypass intended restrictions and access sensitive data or perform malicious actions. For demonstration purposes, let's assume we have a vulnerable usememos/memos repository like so:

.
├───.git
│   ├───hooks
│   ├───info
│   ├───objects
│   └───refs
├───folder1
│   ├───file1.txt
│   └───file2.txt
└───folder2
    └───secret.txt

Now let's say we want to access the secret.txt file, which we don't have the proper access rights to. As an attacker, we can craft a malicious request that abuses this vulnerability to gain access. Here's an example of a malicious request targeting this vulnerability:

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
  -H "Accept: application/vnd.github+json" \
  "https://api.github.com/repos/:owner/:repo/contents/folder2/secret.txt?ref=:branch";

This request is designed to exploit CVE-2023-4696, by targeting the Access and Refresh tokens, and it allows for the unintended viewing of secret.txt.

References to the Vulnerability

For information on the original disclosure of CVE-2023-4696, you can find the official CVE entry here: CVE-2023-4696

Additionally, the GitHub security advisory can be found here: GitHub Advisory

Mitigation Steps

To fix this vulnerability, developers should upgrade their usememos/memos repository to version .13.2 or later. This can be done by simply updating the repository's dependencies, like this:

git checkout master
git pull origin master
npm install usememos/memos@.13.2

Once the update has been applied, it is essential to test your application to ensure that no other dependent features have been affected. Be sure to consider edge cases and proper access control rules when testing.

It is highly recommended also to review access control configurations on your GitHub repositories, ensuring that only authorized users have the necessary permissions and that any disused accounts and tokens are revoked.

Conclusion

In conclusion, improper access control vulnerabilities, such as CVE-2023-4696, are serious security issues that should be addressed as soon as possible. Attackers can potentially access sensitive data and carry out malicious actions when such vulnerabilities are exploited. As a developer or repository owner, it is crucial to stay informed regarding the latest security advisories and update affected dependencies accordingly. By following proper mitigation steps and regularly reviewing access control configurations, you can help protect your repositories from unauthorized access and security threats.

Timeline

Published on: 09/01/2023 01:15:00 UTC
Last modified on: 09/01/2023 13:06:00 UTC