CVE-2020-25720: Unintended Privilege Escalation in Samba due to Insecure Object Creation

A security vulnerability was recently discovered in Samba, a popular software suite that provides file and print services for various Windows-compatible clients. The vulnerability, labeled as CVE-2020-25720, could potentially allow a malicious delegated administrator to escalate their privileges, leading to unauthorized access to sensitive information or even compromising the entire system. In this post, we will explore the details of this vulnerability, including some sample code snippet to demonstrate how this issue can be exploited, links to original research resources, and mitigation recommendations to keep your system protected.

Vulnerability Details

The root cause of CVE-2020-25720 is associated with a flaw in Samba's handling of object creation requests in Active Directory. Specifically, when a delegated administrator has been given permission to create new objects, they are also granted the ability to write to all attributes of that object, including security-sensitive ones. This occurs because the Access Control List (ACL) is not set properly during the object's creation, allowing the delegated administrator to be recognized as the 'creator owner' and retain significant rights to the object.

In simpler terms, this vulnerability results from the fact that a delegated administrator's ownership of a created object can potentially extend to areas that may not be well understood, posing a major security risk.

Exploit Example

To further illustrate the issue, let's look at a sample code snippet that demonstrates how CVE-2020-25720 can be exploited in practice. Suppose the delegated administrator has permission to create a new user object in Active Directory:

# Setting the initial creation permissions
permission_mask = KirkReadControl | KirkWriteDac | KirkCreateChild | KirkDeleteChild

# Creating the new user object
new_user = create_ad_object(parent_object, "CN=New User", permission_mask)

# Modifying the security attributes of the new object's ACL
new_user_acl = get_acl(new_user)
new_user_acl.add_inheritable_aces("Newly Created Object", permission_mask)
set_acl(new_user, new_user_acl)

In this example, the delegated administrator is granted the permission to create a new user object, but the ACL of the new object is also modified immediately to include inheritable ACEs (Access Control Entries). This means that the delegated administrator now has the ability to not only write to all attributes of the object but also modify the object's ACL, effectively granting themselves elevated privileges.

Links to Original References

For a more in-depth understanding of CVE-2020-25720, we recommend reading the full security advisory provided by Samba:

- Samba Security Advisory: CVE-2020-25720

In addition, you may find the following external resources helpful for further information

- CVE details: CVE-2020-25720
- National Vulnerability Database (NVD) entry: CVE-2020-25720

To protect your systems from this vulnerability, follow the steps outlined below

1. Update your Samba installation to the latest available version, which includes the necessary security fixes for CVE-2020-25720. You can find the update information on the official Samba website: Samba Download

2. Assess your existing delegated administrator permissions and ensure that they are granted only the minimum necessary privileges. You may also consider implementing more granular access controls to limit the potential impact of this vulnerability.

3. Regularly monitor your Active Directory infrastructure and log activities to detect any unauthorized access attempts or changes to system files and settings.

Conclusion

The CVE-2020-25720 vulnerability poses a significant security risk for Samba-enabled systems, potentially allowing attackers to exploit delegated administrator permissions and gain unauthorized access to sensitive information. By promptly updating your software and applying recommended mitigation measures, you can protect your systems from this threat and maintain a secure environment.

Timeline

Published on: 11/17/2024 11:15:04 UTC
Last modified on: 11/21/2024 20:51:52 UTC