Best practice guidance

Introduction

Following a recent pen testing workstream on the LocalGov Drupal (LGD) distribution, this document provides detailed guidance on security best practices to be considered during the installation and configuration of LocalGov Drupal. It aims to provide comprehensive and practical advice to ensure that the LocalGov Drupal installation is secure and adequately protected against potential threats.

The security of a LocalGov Drupal installation is paramount, and it is essential to follow the best practices outlined in this document to ensure that the installation is adequately secured. Failure to implement these best practices could expose the installation to security risks and potential data breaches.

It is important to note that security threats are continually evolving, and as such, it is critical to keep abreast of the latest security trends and update the security practices accordingly. This document will provide a starting point for securing the LocalGov Drupal installation, but it should not be considered a complete solution.

By following the security best practices outlined in this document, LocalGov Drupal users can significantly reduce the risk of security incidents and ensure that their installation is adequately protected against potential threats. It is essential to review and implement these security practices regularly to ensure that the installation remains secure and up-to-date.

Findings and Guidance

This document is structured as a list of the findings from the pen test, with an explanation of each finding and a best practice recommendation to mitigate the associated threat.

1. Issue reported to Drupal security team

Explanation

This issue was reported privately to the Drupal security team and is being handled by them.

Best practice recommendation

Apply security updates in a timely manner as they become available.

2. Malicious File Upload

Explanation

Malicious file upload can allow attackers to upload executable or malicious code. If a malicious actor can upload malware, the malicious actor could run that malicious code on the server itself or use it to perform client-side attacks against other web application users or Administrators that might access the file.

Best practice recommendation

LocalGov Drupal, like Drupal core, restricts file uploads to a defined set of file types, which does not include executable files. This makes it difficult in practice for malware to spread via the file upload functionality, as the user would have to take an additional step to make the malicious file executable, and would have to bypass warnings from the operating system in order to do so.

However, this is a possibility, and there is also the possibility of a vulnerability existing in some software that processes a normally non-executable file that would allow code execution. If these risks require treatment in your threat model, it is possible to add antivirus scanning using the ClamAV module. Note that the module won't do anything by itself - you also need to install the ClamAV antivirus software on your server. The module can then be configured to use that installed antivirus software to scan files that are uploaded by your users.

3. Missing Anti-Scripting Controls

Explanation

Web applications process numerous calls from multiple clients, but there is a limit to the number that they can handle within a certain time. As the number of concurrent calls increases, the web application may reach that limit, which could impact an organisation's service uptime.

Best practice recommendation

Drupal core has some basic rate limiting functionality in the form of the flood service. However, this is only used in a small set of special cases by default.

The Rate Limits module builds on top of this core functionality by allowing you to limit the rate at which a user or an IP address can access the site.

Another approach to anti-scripting is to use a CAPTCHA (a test that attempts to distinguish between human visitors and automated processes). The CAPTCHA module allows you to apply a variety of CAPTCHA technologies (provided by additional add-on modules) to the forms on your site. However, encountering a CAPTCHA can be an unpleasant experience for users, so this solution should be used only as necessary.

4. Weak Password Policy

Explanation

A simple password is also simple to guess. A malicious actor can perform password guessing and access any user account if a strong password policy is not set.

The accepted best practices for password policies have evolved over the years. In 2017, NIST (the National Institute of Standards and Technology in the US) published updated guidance covering, among other things, new recommendations on enforcing password complexity and password rotation. Shortly after, the UK's National Cyber Security Centre (NCSC) published their own updated guidance along the same lines. Both sets of guidance reflect modern best practices accepted by security professionals. These include:

  • Don't enforce a minimum number of characters per character class (e.g. uppercase / lowercase letters, numbers and symbols). Instead, enforce a minimum password length, and reject passwords from explicit lists of passwords known or expected to be weak or compromised - for example, dictionary words, previously breached passwords, and context-specific terms such as the username or website name.
  • Don't force users to change their passwords on a regular schedule. Rather, monitor for indications that a password may have been breached, and enforce password changes only when an indication of a possible breach is discovered.

Best practice recommendation

The Password Policy module provides a flexible set of constraints that Drupal and LocalGov Drupal administrators can apply to build their own custom password policies.

In the latest version, different policy requirements are provided by different submodules, many of which are included with the Password Policy module. We recommend enabling at least the following modules:

  • Password Policy (the module that provides the core password policy functionality)
  • Password Username Policy
  • Password Blacklist Policy
  • Password Character Length Policy

Also enable any others that you want. However, we suggest not using the Password Character Types Policy or Password Characters of Type Policy modules, as these would conflict with the NCSC and NIST recommendations.

With the modules enabled, go to the configuration page and create a new policy. We suggest setting the Password Reset Days to zero, again in line with the NCSC and NIST recommendations. After saving the policy you will be able to select the roles to which the policy applies, and to configure constraints. We suggest the following:

  • Use the Password Blacklist constraint to disallow a list of words related to your site - such as the site name and variations thereof.
  • Use the Password character length constraint to disallow passwords that are too short. Drupal core's password strength meter suggests a minimum length of 12 characters, so this may be a good choice for consistency. Do not set a maximum length!
  • Also enable the Password username constraint to disallow passwords containing the user's username (it has no additional configuration options).

If you want to enforce the additional constraint of blocking passwords that are known to have been exposed in data breaches, one way to do this is to install the Password Policy Pwned module. This adds a new constraint, Pwned Passwords, which you can configure to block passwords which have appeared at least once (or, if you prefer, a minimum number of times) in known data breaches.

5. Username Enumeration

Explanation

Username Enumeration occurs when a malicious actor can determine the valid users of an application/system. This vulnerability usually exists on the login or forgot password page of an application, where an error message reveals that a username is present or absent on the system when valid or invalid credentials are entered. After enumerating valid users, a malicious actor can gain access to the system using password guessing or automated brute-force attacks. Username enumeration essentially occurs when an application gives different responses when valid and invalid data in various fields are entered.

Best practice recommendation

The Username Enumeration Prevention module can be installed to make it more difficult to discover usernames and verify the existence of particular accounts. However, as noted on that module's project page, Drupal does not make any particular effort to hide usernames, and it is difficult for a contributed module to fully counteract this.

Those requiring a more comprehensive defence might consider enabling two-factor authentication, which can be added by installing the Two-Factor Authentication (TFA) module.

6. Missing Security Related Headers

Explanation

The application did not implement certain HTTP security headers, which help in protecting the application against attacks including Cross-site Scripting (XSS) and Clickjacking.

Best practice recommendation

While it's possible to configure some HTTP headers using Drupal contributed modules, it's generally better to set them in the web server configuration instead. That way, they can protect your static files as well as pages served by the Drupal application.

Content-Security-Policy

The content-security-policy (CSP) header is a complex and powerful tool. Crafting and maintaining a good CSP can take considerable effort, but the reward is robust protection against XSS and other attacks.

A simple starting point may look something like this:

content-security-policy: frame-ancestors 'none'; upgrade-insecure-requests

This instructs the browser to prevent the site from being displayed inside a frame (which is important for preventing clickjacking attacks), and to upgrade insecure (HTTP) subrequests to HTTPS rather than simply blocking them.

To get the full benefit of CSP, you would want to add some of the directives that are available for restricting the possible sources of various types of resources that your site can reference. For example, to prevent loading scripts from external sources, you can add the script-src 'self' directive. This is a delicate balancing act, however. An overly restrictive CSP can break some of your site's functionality. Mozilla's Laboratory extension for Firefox is a handy way to experiment with different CSP directives and the effects they may have.

MDN has a more complete list of the available CSP directives.

Permissions-Policy

The permissions-policy header allows you to selectively disable or restrict certain browser features on your site. This can be a security improvement as some features may occasionally have exploitable bugs or unexpected behaviours that can impact your site's security.

Unfortunately there is no way to globally disable all optional features and enable only the ones you want - you must instead explicitly disable every feature that you don't use. MDN has a partial list of directives. You can disable a set of features with a header like the following:

permissions-policy: encrypted-media=(),interest-cohort=()

The above example disables the encrypted-media and interest-cohort features. You can add additional directives to the header to disable other unnecessary or unwanted browser features.

Referrer-Policy

The referrer-policy header allows you to restrict what information the browser shares with other domains that you link to.

In modern browsers this defaults to strict-origin-when-cross-origin, which is generally a pretty safe default: it shares the full referring URL when you link to your own site, but only the origin (i.e. excluding the path and query string, which may contain sensitive information) when linking externally, and nothing at all when linking to a less secure URL (i.e. to a http:// link from your https:// site).

For additional protection in some older browser versions, you can specify this default explicitly:

referrer-policy: strict-origin-when-cross-origin

Alternatively, if you prefer to share as little information as possible with third parties, you can specify same-origin instead.

Note that unlike the older Referer header, the word 'referrer' in the Referrer-Policy header should be spelled correctly.

7. Verbose Error Messages

Explanation

Verbose error message is when the application throws sensitive error messages such as stack traces, database queries or dumps and error codes. These error messages can be the first line of attack where an attacker is able to get the information about the application's underlying technology like the software or framework name and versions. An attacker can accordingly search for vulnerabilities and exploits to harm the application or system, users, and technology.

Best practice recommendation

LGD, like Drupal core, enables the display of verbose error messages by default, to assist in debugging during initial development.

The configuration page at /admin/config/development/logging can (and should) be used to disable the display of error messages before promoting a site to production.

8. Insufficient Session Timeout

Explanation

Session timeout occurs when a user does not perform any action on the website in the given time frame or logs out of the application. This time is set at the web server. Application not having a timeout or having an insufficient session timeout can lead to the misuse of the session ID where a malicious actor can steal or reuse any user's session identifiers. A session must be invalidated on the server side once a user logs out or leaves the session idle.

Best practice recommendation

There are several contrib modules that can be used to enforce a shorter session timeout than the default. One such module is the Automated Logout module, which allows you to set different timeouts per role. This is useful because it allows you to set a shorter timeout for highly-privileged roles to protect your site's security, while setting a longer timeout for less-privileged roles to avoid unnecessarily inconveniencing your users.

9. Weak Account Lockout Mechanism

Explanation

With an insufficient account lockout policy, malicious actors could perform automated dictionary or brute-force attacks against the user and administrative accounts. In a brute-force attack, a malicious actor will guess many passwords rapidly, looking for one password that matches the account password. These attacks often use dictionaries of the most commonly-used passwords, such as "password", "12345", or the season and the year, as well as passwords obtained from previously leaked data breaches.

Best practice recommendation

While a stronger account lockout may indeed provide better defence against brute-force and credential stuffing attacks, it would also open an easy vector for denial-of-service attacks against individual accounts.

Our recommendation is to rely on other approaches to preventing brute force and credential stuffing attacks, such as enabling two-factor authentication and preventing the use of known-compromised passwords.

10. Verbose HTTP Response Headers

Explanation

In its default configuration, the application occasionally displays the server technology or CMS that it utilises. This provides the actual version data in some cases and merely the technology name in others. In any situation, it is critical to carefully regulate the data provided in both the HTTP response header and the HTTP response body to ensure that no technical or server details are present.

Best practice recommendation

It is generally possible for a determined attacker to identify the server technology and CMS by other means than HTTP response headers. Obscuring this information may deter some low-effort opportunistic attackers. However, there are some headers that are unique to Drupal (e.g. X-Drupal-Dynamic-Cache) that cannot be disabled without sacrificing some functionality. Accordingly, we do not recommend obscuring HTTP response headers as a standard practice. However, if you can live without the dynamic page cache, you can obscure the other identifying headers (Server and X-Generator) by setting fixed values for them in your web server configuration.