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Account Takeover Protection and WAF mitigations to help stop Global Brute Force Campaigns


4 min read
Account Takeover Protection and WAF mitigations to help stop Global Brute Force Campaigns

Earlier today a cybersecurity advisory was published by international security agencies identifying widespread attacks against government and private sector targets worldwide. You can read the full report here, which discusses widespread, distributed, and anonymized brute force access attempts since mid-2019 and still active through early 2021.

Today, we have rolled out WAF mitigations to protect our customers against these types of attacks.

And we are making the exposed credential check feature of Account Takeover Protection available to all paid plans at no additional charge today. We had been planning to release these features later this month to a subset of our customers, but when we were informed of this ongoing attack we accelerated the release timeline and expanded those eligible to use the protections.

The attack which we are now protecting against was carried out in three main steps:

  1. Initial account compromise performed via brute force attacks against authentication endpoints;
  2. Once access was gained, network traversal was performed leveraging several publicly known vulnerabilities, including but not limited to CVE 2020-0688 and CVE 2020-17144 that widely affected Microsoft Exchange Servers;
  3. Deployment of remote shells, such as a variant of the reGeorg web shell, and network reconnaissance to gather additional information;

Detecting Brute Force Login Attempts

The findings in the report highlight the increasing problem of password reuse and compromise that affects online applications, including government and large private sector online properties.

In March 2021, during Security Week, we launched a beta program for a new feature called Exposed Credential Checks. This feature allows website administrators to be notified whenever a login attempt is performed using a breached username and password credential pair. This is a very strong signal to enforce two factor authentication, a password reset, or simply increase user logging for the duration of the session.

Starting today, all paid plans (i.e., Pro and above) can enable the exposed credential check feature of Account Takeover Protection. We made the decision to give this to more customers due to the severity of the report and ongoing nature of the exploitation attempts.

While we work to accelerate the automatic deployment of the capability across these plans, you can file a support ticket with “Account Takeover Protections activation request” in the subject line to have it manually enabled today for your domains.

Customers who are not yet running the new WAF announced during Security Week will first be upgraded to this version; all accounts created after May 6, 2021, are already on the new version. The exposed credential managed ruleset can then be turned on with a single click, and supports the following applications out of the box:

  • WordPress
  • Joomla
  • Drupal
  • Ghost
  • Magento
  • Plone
  • Microsoft Exchange

When turned on, whenever a compromised credential is detected the following header will be added to the request to the origin server:

Exposed-Credential-Check: 1

This header alone won’t provide additional security, but can be used by the origin server to enforce additional measures, for example forcing a two factor authentication or password reset flow. The feature can also be deployed in logging mode to easily identify brute force attacks targeting your application using the Firewall Analytics dashboard.

If your application is not in the default set of protected applications, as long as your login endpoints conform to one of our generic rules, the feature will work as expected. We currently have two options:

  • A JSON endpoint (application/json) that submits credentials with 'email' and 'password' keys, for example {“email”:”[email protected]”, “password”:”pass”}
  • A standard login HTML form (application/x-www-form-urlencoded), under a URL that contains “login”. The form fields should be named username and password respectively;

Developer documentation can be found here.

WAF Rule Update

In addition to exposed credential checks, we have implemented improvements to the following WAF rules effective immediately:

  • Improved rule 100197
  • Added a new rule 100197B (default disabled)

These rules will match against request payloads that contain the reGeorg shell variant mentioned in the report. The rule improvements were based on, but not limited to, the Yara rule found in the security advisory. In summary the rule will block payloads which contain the following signatures and similar variations:

%@ Page Language=C#

Additional Mitigations

In addition to monitoring and defending against credential stuffing attacks using datasets of compromised credentials, security administrators should implement additional best practices for their authentication endpoints. For example, multi-factor authentication, account time-out and lock-out features, and stronger methods of authentication that require “having” something such as a hard token or client certificate—not just “knowing” something such as a username and password.

Cloudflare has a number of additional features that customers are also advised to deploy where possible on their environments to strengthen their security posture:

  • Cloudflare Access can be used to provide strong, multi-factor authentication for both internal and external facing applications, and integrates directly with your organization’s SSO and identity providers (IdP);
  • Where possible, implementing Mutual TLS rules (mTLS) in front of authentication endpoints will increase an application security posture considerably by avoiding the use of passwords. This can be done both as a Firewall Rule or as an option when setting up Cloudflare Access;
  • We recently announced a Managed IP list that will contain Open Proxy endpoints identified by Cloudflare’s intelligence - this list can be used when creating Firewall Rules to protect authentication endpoints by issuing Captcha (or other) challenges;
  • The use of our Bot Management detection has recently been expanded to all self-serve paid plans via our Super Bot Fight Mode product - this product allows customers to set up rules to challenge/block automated traffic, such as bots attempting brute force attacks, while letting verified bots access Internet properties normally.


Brute force attacks are a prevalent and successful means to gain initial access to private networks, especially when applications require only username and password pairs for authentication. The report released today reinforced the widespread use of these credential stuffing attacks to gain access and then pivot to additional sensitive resources and data using other vulnerabilities.

Cloudflare customers are protected against these automated attacks by two new WAF rules, and also through the exposed credential check feature of our Account Takeover Protection offering. We have made the exposed credential check feature available today, to all paid plans, in advance of our planned launch later this month. Reach out to our support team immediately if you would like this feature enabled as we work to turn it on for everyone.

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Michael Tremante|@MichaelTremante

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