How to Block Anonymizing Services using Okta

Moussa Diallo and Brett Winterford

Summary: Every customer using the Workforce Identity Cloud and Customer Identity Solution can now block access requests originating from anonymizing services prior to authentication.

Over the last month, Okta has observed an increase in the frequency and scale of credential stuffing attacks targeting online services, facilitated by the broad availability of residential proxy services, lists of previously stolen credentials (“combo lists”), and scripting tools.

  • From March 18, 2024 through to April 16, 2024, Duo Security and Cisco Talos observed large-scale brute force attacks on multiple models of VPN devices.

  • From April 19, 2024 through to April 26, 2024, Okta’s Identity Threat Research team observed a spike in credential stuffing activity against user accounts from what appears to be similar infrastructure.

In credential stuffing attacks, adversaries attempt to sign-in to online services using large lists of usernames and passwords obtained from previous data breaches of unrelated entities, or from phishing or malware campaigns.

All recent attacks we have observed share one feature in common: they rely on requests being routed through anonymizing services such as TOR. Millions of the requests were also routed through a variety of residential proxies.

What is the Tor Network?

Tor (The Onion Router) provides its users a method of sending requests to web sites in which the originating source IP address of the request is obscured. Tor relies on the relay of messages across an overlay network of “onion routers”, each of which can only observe the IP of the preceding node and the next node in the communication. While Tor has legitimate uses, it is routinely used to conceal the real IP address of attackers.

What are Residential Proxies?

Residential Proxies are networks of legitimate user devices that route traffic on behalf of a paid subscriber. Providers of residential proxies effectively rent access to route authentication requests through the computer, smartphone or router of a real user, and proxy traffic through the IP of these devices to anonymize the source of the traffic.

Residential Proxy providers don’t tend to advertise how they build these networks of real user devices. Sometimes a user device is enrolled in a proxy network because the user consciously chooses to download “proxyware” into their device in exchange for payment or something else of value. At other times, a user device is infected with malware without the user’s knowledge and becomes enrolled in what we would typically describe as a botnet. More recently, we have observed a large number of mobile devices used in proxy networks where the user has downloaded a mobile app developed using compromised SDKs (software development kits). Effectively, the developers of these apps have consented to or have been tricked into using an SDK that enrolls the device of any user running the app in a residential proxy network.

The net sum of this activity is that most of the traffic in these credential stuffing attacks appear to originate from the mobile devices and browsers of everyday users, rather than from the IP space of VPS providers. For more information on residential proxy services, we recommend this informative summary by CERT Orange Cyberdefense and Sekoia.

Block it at the Edge

One of the key tenets of the Okta Secure Identity Commitment is to champion customer security best practices. We are committed to raising the bar for default security features in our platforms.

In February 2024, Okta released a well-timed capability into the Workforce Identity Cloud (WIC) and Customer Identity Solution (CIS) that detects and blocks requests from anonymizing services.

This Early Access feature can be turned on at Settings > Features in the Okta Admin Console.

Organizations that wish to deny access from specific anonymizers, and allowlist others, must be licensed to use Dynamic Zones (part of Adaptive MFA). Expect enhancements to this feature over the weeks ahead.

Customers using the Customer Identity Cloud (Auth0) should consider the Attack Protection Suite, and consider the other recommendations in the table below.

Modern Defenses, Built into the Identity Platform

The unprecedented scale of these attacks has provided clear insights into the controls most effective against credential stuffing.

ThreatInsight, Okta’s built-in control against high volume attacks, blocks requests from IPs involved in large scale credential based attacks prior to authentication.

The small percentage of customers where these suspicious requests proceeded to authentication shared similar configurations: The Org was nearly always running on the Okta Classic Engine, ThreatInsight was configured in Audit-only mode (not Log and Enforce mode), and Authentication policies permitted requests from anonymizing proxies.

Customers using Okta Identity Engine that (a) enabled ThreatInsight in log and enforce mode and (b) deny access requests from anonymizing proxies were protected from these opportunistic accounts. These basic features are available in all Okta SKUs. Upgrading to Okta Identity Engine is free, often highly automated, and provides access to a range of features including CAPTCHA challenges for risky sign-ins and passwordless authentication using Okta FastPass.

Broader Recommendations

We recommend Okta customers practice defense in depth to mitigate the risk of account takeovers from credential stuffing attacks.


Workforce Identity Cloud (Okta)

Customer Identity Cloud (Auth0)


Embrace Passwordless 


Okta FastPass


FIDO2 WebAuthn



as a preferred sign-in method


Prevent users from making poor password choices

Require 12 chars and no parts of username in

Password Policy

. Block passwords found in

common password list


Breached Password Protection


Credential Guard

to prevent use of passwords known to have been breached in 3P sites


Enforce MFA on sign-in

Require MFA in Global Session Policies

Require MFA for Password Authentication flows


Deny requests from locations where your organization does not operate


Network Zones

to block requests prior to authentication

Deny access by location using a WAF or via the Country-based Access Control



Deny authentication requests from IPs with poor reputation

Deny requests made via anonymizing services (Early Access) or via

Dynamic Network Zones





log and enforce

mode to deny attempts based on the volume and velocity of failed requests from an IP



challenges on high risk logins


Suspicious IP Throttling

to slow down login attempts from suspicious IPs


Bot Protection

to present CAPTCHA challenges to requests from suspicious IPs

Use 3P

Auth0 Actions

integrations to check if an IP is associated with an anonymizing proxies 


Monitor for and respond to anomalous sign-in behavior

Enforce per-user

Account Lockout

. Exempt requests from devices that have successfully authenticated

Monitor for


events and rate limit violations 


Brute-force Protection

to block and lockout accounts subject to persistent failed authentication requests 

Monitor for sign-in events using invalid usernames/non-existent users and/or previously breached passwords

TTPs used in Recent Attacks

Top 20 ASNs

Autonomous System Number

Network Provider


FranTech Solutions


Quintex Alliance Consulting


Stiftung Erneuerbare Freiheit




1337 Services GmbH


netcup GmbH








Universal Layer LLC


FlokiNET ehf


1984 ehf


Pfcloud UG


The Calyx Institute


Private Layer INC


TerraHost AS




Foundation for Applied Privacy


Akamai Connected Cloud


KeFF Networks Ltd

User Agent

Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Firefox/102.0

Relevant System Log Queries: Workforce Identity Cloud


System Log Query

ThreatInsight has Detected Access Requests from IPs Associated with Suspicious Behavior

eventType eq "security.threat.detected"

Suspected Brute Force Attack (T1110.001)

eventType eq "security.threat.detected" AND outcome.reason eq "Login failures"

Suspected Credential Stuffing Attack (T1110.004)

eventType eq "security.threat.detected" AND outcome.reason co "Login failures with high unknown users count"

Suspected Password Spray Attack (T1110.003)

eventType eq "security.threat.detected" AND outcome.reason co "Password Spray"

Targeted Brute Force Attack against a Specific Org

eventType eq "security.attack.start"

Relevant System Log Queries: Customer Identity Cloud (Auth0)


Log Query

Failed login request


Failed login: Invalid username/email address


Failed login: Invalid password


Login attempt from a known leaked password


Signup (registration) attempt from a leaked password


IP address blocked: excessive failed login or registration requests without a successful login


User account lockout: excessive failed login requests per time period from the same IP address


IP address blocked: excessive failed login attempts to a single user account


Moussa Diallo
Sr Manager, Identity Threat Research
Brett Winterford
Regional CSO, Okta APJ
Brett Winterford is the regional Chief Security Officer for Okta in the Asia Pacific and Japan.
He advises business and technology leaders on evolving threats and helps them harness advances in identity technology to drive business outcomes and mitigate risk.
Prior to Okta, Brett held a senior security leadership role at Symantec, and helmed security research, awareness and education at Commonwealth Bank.
Brett is also an award-winning journalist, having long ago been the editor-in-chief of iTnews Australia and a contributor to ZDNet, the Australian Financial Review and the Sydney Morning Herald. Most recently, he was the founding editor of the Srsly Risky Biz newsletter, a companion to the Risky Business podcast, providing the cybersecurity, policy, defense and intelligence communities with a weekly brief of the news that shapes cyber policy.