Credential Stuffing

An attacker buys a list of leaked credentials from a data breach and points an automated script at your login page. Thousands of username/password combinations get tested per hour. Most fail, but a small percentage work because some people reuse passwords. Those accounts are now compromised. Traditional defenses barely slow this down, but Dregs catches it quickly.

The Credential Stuffing Attack Vector

Data breaches are constant. Billions of username/password pairs are circulating on the "dark web", and attackers know that a significant percentage of people reuse the same password across multiple services. Credential stuffing exploits this vulnerability at scale. Automated scripts gather leaked credentials from one breach and test them against every login form they can find... including yours.

The math works in the attacker's favor. Even a 0.1% success rate on a list of 100,000 credentials means 100 compromised accounts. Running the attack costs next to nothing — a cloud VM, a proxy list, and an off-the-shelf stuffing tool. The credentials are often free or cheap. And the payoff per compromised account can be substantial.

The standard defenses in most web applications aren't designed for this type of attack.

IP rate limiting Distributed botnets use thousands of residential IPs, keeping each one well under your thresholds

Account lockout Locks out legitimate users who haven't done anything wrong, and might deny your own customers

Password complexity rules Good idea, but useless when the password being tested is "strong" but the customer is reusing it

WAFs Signature-based rules miss low-and-slow attacks that stay within rate limit thresholds

Login CAPTCHAs Add friction to legitimate users, while CAPTCHA farms solve them for fractions of a cent

These traditional defenses either punish your real users, fail against distributed attacks, or both. You need detection that looks at what the visitor actually is — not just what they're doing on a single request.

How Credential Stuffing Threatens Your Business

A significant credential stuffing campaign doesn't just compromise a few accounts — it creates cascading damage across your entire operation.

Account takeover

Compromised accounts may lead to fraud, unauthorized purchases, data theft, and legal liability. Each taken-over account is a breach incident that may trigger notification obligations, depending on your jurisdiction and what data was breached.

Lost customer trust

Users who discover their account was accessed by someone else lose confidence in your platform. Even if it was ultimately their fault for reusing credentials, the trust damage ultimately extends far beyond the directly affected accounts.

Operational burden

Support tickets flood in. Incident response teams scramble. Forced password resets frustrate users who weren't even affected. Every credential stuffing incident costs engineering, support, and leadership time that should be spent building your product.

How Dregs Detects Credential Stuffing

Credential stuffing attacks have a distinctive pattern that's visible across multiple dimensions simultaneously. The login credentials might be correct, but everything else about the visitor screams automation. Dregs scores multiple dimensions at once.

Humanity Score

Automated login scripts leave fingerprints that betray their true nature. The Humanity score catches headless browsers, scripted environments, and automation frameworks through device characteristics that are hard to fake — hardware profiles, rendering behavior, browser API availability, and timing signatures. Even sophisticated stuffing tools running in real browsers produce fingerprints that differ from genuine human sessions.

Behavior Score

Credential stuffing has a behavioral profile that's impossible to hide. The Behavior score detects rapid-fire login attempts, unnaturally consistent timing between submissions, sessions that do nothing but submit login forms, and interaction patterns that no real user would produce. Even with randomized delays, the velocity and uniformity of a stuffing attack often stands out against normal login behavior.

Device fingerprint showing one device cycling through many different login identities

Device Fingerprinting

A credential stuffing attack uses one device (or a small pool of devices) to attempt logins across many different accounts. Device fingerprinting makes this pattern immediately visible. The same fingerprint appearing in login events for hundreds of different usernames is a signal that no amount of IP rotation or user-agent spoofing can hide.

Uniqueness Score

The Uniqueness score measures how distinct a visitor is from other visitors. A device that cycles through hundreds of different identities in a short window produces an obvious signal that's the opposite of real user behavior. This cross-identity analysis is often one of the strongest indicators of credential stuffing attacks.

Example: Handling a Credential Stuffing Attack

Here's what it looks like when a credential stuffing campaign targets your login page in the middle of the night:

2:00 AM

A new device arrives at your login page. Dregs collects the device fingerprint on first page load — before any login form is submitted.

2:01 AM

50 login events hit in 60 seconds, all from the same device fingerprint, each with a different username. The Humanity score drops to 5 — the timing between attempts is mechanical, with no natural variance.

2:01 AM

The Behavior score drops to 3. The session contains nothing but login form submissions at impossible velocity. The device is now associated with dozens of different identities — the Uniqueness score collapses.

2:01 AM

Dregs assigns a "Credential Stuffing" badge based on the combined scores. A critical alert fires to your monitoring channel. A webhook notifies your application, which blocks the device's IP and terminates the session before the attacker gets through even a fraction of their credential list.

The attack was detected and stopped within a minute. Any accounts that were successfully accessed during that window can be automatically flagged for forced password reset.

Mitigating Credential Stuffing Attacks

Detection is only half the equation. Once Dregs identifies a credential stuffing attack, your team needs to act on it fast. Different stages of the attack call for a combination of automated and manual responses.

Session blocking

Terminate and block affected sessions immediately. The stuffing tool loses its connection and has to start over from scratch — if it can get past detection again at all. This is the fastest way to stop an active attack and protect other user accounts that haven't been breached yet.

Account protection

Force an immediate password reset on any account that was successfully accessed during the attack. Notify the affected users. Invalidate existing sessions. Act quickly to limit the damage window and prevents the attacker from using compromised credentials later.

IP blocking

Block the source IP address or range at the network level. While sophisticated attackers rotate IPs, many credential stuffing operations use a limited pool. Quickly blocking the bad IPs reduces the volume of attempts and forces the attacker to burn through their proxy infrastructure faster.

Dregs can notify your team with alerts and webhooks, depending on your preferred notification channels. This gives you a chance to react quickly to credential stuffing attacks and other unusual behavior. Get notified quickly, whether the attack happens at 2 AM on a Tuesday or noon on a holiday.

Stop credential stuffing before accounts get compromised.

Dregs detects anomalies like automated login attacks so your team can respond quickly. Install the tracking script and start protecting your site.

Schedule a Demo