Credential stuffing isn’t new, but it is making a comeback. With identities spread across more SaaS apps than ever, and a growing pool of leaked credentials available on the dark web, attackers are leaning on this tried-and-true tactic to breach systems quickly and quietly.
This attack method has been behind countless breaches, from global enterprises to small SaaS startups. And it’s easy to see why: it works. With billions of leaked credentials floating around the dark web, attackers don’t need to break in. They just log in.
Credential stuffing is simple, scalable, and alarmingly effective when identity protection isn’t a priority. In this article, we’ll break down how credential stuffing works, why SaaS environments are such easy targets, and what your team can do to shut it down.
What is credential stuffing?
Credential stuffing is a type of cyberattack in which attackers use stolen username and password combinations,usually harvested from previous data breaches,to try and access user accounts on other platforms. Because many people reuse passwords across services, it’s surprisingly effective. Unlike brute-force attacks that guess credentials, credential stuffing relies on using valid credentials, which makes it harder to detect with conventional login security tools.
These attacks are typically automated. Attackers deploy bots or scripts to cycle through large lists of stolen credentials across popular SaaS apps, waiting for a match. Once they find one, it can lead to a much broader compromise. Successful logins often become the starting point for deeper exploitation, including privilege escalation, sensitive data exfiltration, and lateral movement.
Why SaaS is a prime target
SaaS applications are where business lives. From email and document sharing to password repositories, CRM tools, financial systems, and project management platforms, SaaS is at the core of every team’s day-to-day work. That centrality makes it a high-value target. More critically, the way SaaS is structured, makes it uniquely vulnerable to credential stuffing.
Most SaaS platforms authenticate users through single sign-on (SSO). That means access hinges on the strength of the user’s credentials and any secondary factors like MFA. But when attackers have a valid username and password, and if MFA is weak or missing, that barrier becomes dangerously thin. Even with MFA in place, attackers can exploit other weaknesses, like session hijacking or phishing for second-factor authentication codes.
Password reuse is another major issue. Despite awareness efforts, many users continue to use the same or similar passwords across platforms. When a breach occurs on one site, those credentials often work elsewhere. In a SaaS environment where everything is interconnected, the risk compounds quickly.
Shadow IT also plays a role. Employees often adopt SaaS tools without going through security reviews. These unapproved apps may not follow strong security practices and may not be monitored by central security teams. That makes them an ideal entry point for attackers using credential stuffing.
Recognizing the signs of credential stuffing
Credential stuffing isn’t always immediately obvious. Because it involves the use of valid credentials, many traditional alerting systems may not catch it. However, there are behavioral signals that can indicate this type of attack.
One of the clearest signs is a spike in failed login attempts across multiple user accounts, often coming from the same IP address or IP range. This may be accompanied by logins from unexpected locations or countries where the organization has no presence. Sometimes, an increase in MFA prompts or account lockouts can signal that attackers are attempting to authenticate en masse.
After a successful login, attackers often move quickly. Look for abnormal user behavior, such as access to unfamiliar applications, data exports, or permissions being modified. These are signs that an attacker may have gained access through credential stuffing and is now attempting to expand their reach.
Prevention: What works and what doesn’t
Preventing credential stuffing requires a layered approach that combines strong authentication practices, behavior monitoring, and modern detection tools. Relying on a single control,like enforcing long passwords,isn’t enough.
Start with multi-factor authentication (MFA). MFA significantly reduces the risk of credential-based compromise by adding another layer of verification. While not foolproof, it makes automated attacks much harder to scale.
Implementing single sign-on (SSO) and encouraging the use of password managers can also reduce password reuse and simplify user experience. SSO gives security teams a single control point for managing access, and password managers encourage users to generate strong, unique passwords.
Rate limiting and CAPTCHA mechanisms can be useful for slowing down or deterring automated login attempts. These tools work best at the network edge, blocking bots before they get too far. However, attackers are becoming increasingly sophisticated at bypassing these measures, especially with the use of residential proxies and human-in-the-loop CAPTCHA solving services.
Another important step is auditing and cleaning up stale accounts. Dormant users with valid credentials are often overlooked but provide a wide-open door for attackers. Regularly reviewing and removing unused accounts reduces your exposure.
User education remains a key part of the defense strategy. Teaching employees not to reuse passwords and to recognize phishing attempts can make a real difference. But it’s not enough on its own. Awareness needs to be backed by policy and tech.
How identity threat detection and response factors in
Even with good prevention practices in place, some credential stuffing attacks will succeed. That’s why detection and response are just as important. Identity Threat Detection and Response (ITDR) is specifically designed to uncover identity-based threats like credential stuffing and stop them before they turn into full-blown breaches.
ITDR platforms work by monitoring identity activity across all SaaS applications. They look at login patterns, access behavior, permission changes, and other signals to detect when something is off. This is especially important when an attacker has valid credentials,because the activity looks normal on the surface, traditional security tools may not flag it.
Wing Security’s ITDR solution goes a step further by building identity-centric timelines. This means you can track exactly what a user,or attacker,has done across every connected SaaS app, from initial login to privilege escalation to data access. This connected view is essential for understanding and containing threats in real time.
ITDR also enables faster, more confident responses. When a credential stuffing attempt is detected, Wing can automatically isolate the affected identity, revoke tokens, and trigger response workflows. It turns scattered signals into a full attack story and gives your team the context they need to act.
Behavioral analytics adds another layer. By comparing current behavior to historical norms, ITDR can spot anomalies that might otherwise go unnoticed. For example, a login from an unfamiliar location followed by access to sensitive files in an app the user has never used before can be flagged immediately.
The cost of credential stuffing: the 2023 23andMe breach
A major example of credential stuffing in action occurred in 2023, when genetic testing company 23andMe disclosed a breach that affected millions of user accounts. Attackers used credentials obtained from previous breaches to access customer accounts through automated login attempts—a classic credential stuffing strategy. Once inside, they accessed names, birth years, geographic locations, and ancestry details of approximately 6.9 million users.
What made this breach especially impactful was that attackers didn’t need to exploit 23andMe’s infrastructure—they simply used valid logins. From there, they leveraged the company’s DNA Relatives and Family Tree features to extract additional data connected to compromised accounts.
This breach highlights how credential stuffing often serves as a launchpad for more extensive data harvesting, particularly when sensitive personal or behavioral data is involved. It also underscores why authentication alone isn’t enough. Without deeper identity monitoring and anomaly detection, even well-protected accounts can become high-risk entry points.
Why credential stuffing is only the beginning
Credential stuffing is often the first step in a larger campaign. Once attackers gain access, they rarely stop at one account. They use that initial foothold to escalate privileges, harvest data, plant backdoors, and move laterally to higher-value targets.
In SaaS environments where everything is connected, this lateral movement can happen quickly. A compromised marketing tool might be connected to a CRM platform, which in turn has access to financial data or customer records. Without strong identity monitoring, attackers can exploit these connections before anyone notices.
This is why SaaS security strategies must move beyond simple login protection. Identity-based threats require identity-based detection. Credential stuffing might look like a login problem, but it’s really an identity problem.
Protecting your org from credential stuffing
Credential stuffing continues to be one of the most effective and overlooked attack vectors in SaaS. It exploits the simplest weakness, reused credentials, and turns it into a wide-open door for deeper compromise.
Stopping it requires more than a strong password policy. It demands identity-level visibility, contextual analysis, and fast, automated response. That’s where ITDR comes in.
SaaS security starts with understanding who has access to what, and how that access is being used. The sooner you can spot something that doesn’t belong, the sooner you can stop it from spreading.
Want to see how Wing helps detect and stop credential-based attacks before they escalate? Explore our ITDR solution.