Credential stuffing attacks are rising fast—and the consequences are escalating just as quickly.
Every reused password or phishing click is another crack in your organization's defenses. And with VPNs and remote access gateways exposed to the public internet, even a single compromised login can lead to massive data leaks or system-wide breaches.
This post will explain what credential stuffing is and how it works, distinguishing it from brute force attacks by emphasizing its use of real, stolen credentials rather than guesswork. We'll examine why VPNs and remote access portals are especially attractive targets for these attacks, given their public-facing nature and reliance on passwords. You'll also learn the best practices for defending against credential stuffing, including implementing multi-factor authentication (MFA), rate limiting, IP reputation filtering, and user education around credential hygiene. Finally, we’ll cover how OpenVPN solutions can reinforce your security posture with built-in features designed to detect and prevent these types of attacks.
What Is Credential Stuffing and Why Does It Matter?
The Open Web Application Security Project (OWASP) defines credential stuffing as the automated injection of breached username/password pairs in order to fraudulently gain access to user accounts.
Unlike brute force attacks—which rely on guessing credentials—credential stuffing uses known, stolen login details that still work because people reuse passwords. Often.
In fact, over 60% of people admit to reusing the same passwords across multiple platforms. That bad habit gives attackers a real edge, especially since over 15 billion credentials are already circulating on the dark web.
And it's not just a user problem. According to Verizon’s 2022 Data Breach Investigations Report, more than 80% of breaches now involve stolen or weak credentials.
In short: Human behavior is your biggest threat vector—and your first line of defense.
Credential Stuffing vs. Brute Force Attacks
Let’s clear something up: brute force and credential stuffing are not the same thing.
- Brute force attacks try to guess credentials through trial and error.
- Credential stuffing uses real login data obtained from prior breaches.
Credential stuffing is harder to detect because the credentials are valid, and attackers often rotate IPs, mimic legitimate browsers, or use distributed botnets to avoid triggering alarms.
That makes it significantly more dangerous—especially for already overloaded security teams juggling multiple attack vectors.
➡️ Read more about brute force attacks
Role of Phishing in Credential Stuffing
Even if your users never show up in a breach, they might hand over their passwords willingly—thanks to phishing.
Phishing remains one of the easiest ways for attackers to harvest credentials. Once obtained, those same usernames and passwords often grant access to both personal and business accounts.
According to the Ponemon Institute, 51% of people reuse passwords across work and personal platforms, making phishing the perfect on-ramp to a credential stuffing campaign.
➡️ Brush up on phishing awareness
Understanding the Credential Stuffing Lifecycle
Credential stuffing isn’t just one step—it’s an entire attack pipeline. Here's how it works:
Collecting Stolen Credentials
Attackers typically begin by acquiring large troves of stolen credentials. These are often purchased or downloaded from data breach dumps found on dark web marketplaces. To manage and test these credentials efficiently, they use tools like Sentry MBA, which automate much of the process.
Additionally, attackers establish proxy networks and distributed botnets to spread out traffic, helping them avoid rate limits and detection mechanisms.
Mass Testing & Exploitation
Armed with credential lists and anonymized infrastructure, attackers move to the next phase: mass testing. They launch login attempts across a wide array of VPN portals, leveraging scripts and automation to mimic real browser behavior and legitimate traffic patterns. This helps them evade basic detection systems. When valid credentials are identified, attackers store them for deeper exploitation, often escalating access privileges or conducting lateral movement within the targeted environment. Once they’ve confirmed working credentials, they’ve essentially unlocked a door—and they rarely stop at just peeking inside.
Why VPNs and Remote Access Are High-Risk Targets
Credential stuffing attacks don’t just target consumer apps. They target your infrastructure.
Why? Because VPNs and remote access gateways are:
- Exposed to the internet
- Access points to sensitive systems
- Often still secured by passwords alone
That combination makes them ideal targets.
During the COVID-19 remote work surge, Akamai reported a 2,000% spike in credential stuffing attacks aimed specifically at VPNs.
➡️ Learn more about how VPNs support network security
Top Prevention Techniques
There’s no silver bullet for these risks; credential stuffing requires a multi-layered defense strategy. But we do know a few layers that make a powerful difference.
Multi-Factor Authentication (MFA)
MFA stops over 99.9% of credential-based attacks (according to Microsoft). It’s your strongest frontline defense.
Best practices:
- Use phishing-resistant MFA (e.g., FIDO2 or authenticator apps)
- Enforce MFA across all remote access portals
- Use SAML or OIDC for centralized policy management
➡️ Understand the difference between 2FA and MFA
Rate Limiting & CAPTCHA
Slowing down attacks makes them more expensive and less effective.
Best practices:
- Add progressive delays after failed login attempts
- Temporarily block suspicious IPs
- Trigger CAPTCHA challenges after repeated failures
IP Reputation & Geo-Blocking
Credential stuffing often relies on rotating through IP addresses. Fight back with smart blocking.
Best practices:
- Use services to block known malicious IPs and TOR nodes
- Apply conditional access controls based on behavior and location
- Balance friction with usability
Credential Hygiene & User Education
Preventing credential stuffing starts with better passwords.
Best practices:
- Require a company-wide password manager
- Block breached or weak passwords during account creation
- Run regular training on phishing, reuse, and strong credential habits
➡️ See more on password hygiene and IoT vulnerabilities
How OpenVPN Helps Prevent Credential Stuffing
OpenVPN products are built with credential security in mind.
Security Features
Both Access Server and CloudConnexa include robust security features to protect against credential-based attacks. They offer multi-factor authentication (MFA) support compatible with all major identity providers, allowing organizations to enforce strong access controls across remote access points. Integration with LDAP, RADIUS, and SAML ensures that authentication flows are flexible and can be centrally managed. Administrators can also apply group-based access controls to fine-tune permissions based on roles or departments. Additionally, OpenVPN supports certificate-based login options for environments requiring even stricter identity verification.
Advanced Monitoring & Detection
Beyond authentication, OpenVPN platforms include advanced detection capabilities to spot suspicious activity early. These include alerting mechanisms for login anomalies, such as access attempts from unexpected locations or devices. OpenVPN tracks user and device behavior over time, allowing it to identify deviations from normal usage patterns. Velocity monitoring—tracking the speed and frequency of logins—along with geolocation data help surface potential abuse. These systems also integrate with SIEM solutions, empowering security teams to investigate and respond to threats with greater precision and context.
OpenVPN products are built with credential security in mind.
➡️ Explore CloudConnexa for cloud-native credential protection
➡️ Use Access Server for a self-hosted VPN with full MFA support
Security Features
Both Access Server and CloudConnexa include a number of critical capabilities that work together to protect your VPN from credential-based attacks. They support multi-factor authentication (MFA) with all major identity providers, making it easy to enforce strong, secondary verification methods across your organization. In addition, both platforms integrate with authentication protocols like LDAP, RADIUS, and SAML, ensuring compatibility with existing infrastructure and centralizing access control.
Administrators can define group-based access policies to assign permissions based on user roles or responsibilities. This limits unnecessary access and enhances security through the principle of least privilege. Finally, OpenVPN supports optional certificate-based login, giving organizations with higher security demands a way to verify users through device-specific credentials, reducing dependence on passwords altogether.
Advanced Monitoring & Detection
OpenVPN supports multiple advanced detection capabilities to help security teams stay ahead of credential-based threats. These include real-time alerts triggered by login anomalies—such as attempts from unusual locations or devices—which serve as early warning signs of suspicious behavior. The platform also enables detailed tracking of user and device activity over time, allowing for the identification of behavioral deviations that may indicate compromise. Additionally, OpenVPN utilizes velocity and geolocation-based risk scoring to flag access patterns that are inconsistent with typical user behavior. For organizations with centralized logging and analytics tools, OpenVPN offers seamless integration with Security Information.
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