Credential Stuffing (2)

The first part of this series highlighted an often underestimated reality: credential stuffing does not rely on spectacular technical flaws, but on the reuse of valid credentials from sometimes old leaks. This characteristic makes it a lasting threat, hard to detect and perfectly compatible with otherwise well-secured infrastructures.The question is therefore no longer only to understand the phenomenon, but to identify the responses that are truly suitable. Yet in this area, many organizations deploy measures that seem reassuring but whose effectiveness remains limited against attacks designed to look like legitimate use.

How, then, do we fight such a phenomenon?

Moving Away from a Password-Centred Approach

The most common response to credential stuffing is to strengthen password complexity requirements. This measure, although necessary from an overall security perspective, addresses only a marginal part of the problem. As we have seen, credential stuffing above all exploits credentials already compromised elsewhere. In this context, a password's theoretical complexity matters less than its reuse. A long, complex password used on several services remains exploitable once it has leaked once.

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A policy focused exclusively on the formal strength of passwords has several limitations

• it does not take into account the history of external compromises
• it does not make it possible to identify accounts exposed through third-party leaks
• it gives a sense of protection that does not match the real level of risk

The problem of credential stuffing therefore requires a change of perspective: it is no longer only a matter of protecting a secret, but of considering that this secret may already have been exposed elsewhere.

Multifactor Authentication: Necessary but Insufficient

Multifactor authentication is one of the most effective levers for reducing the impact of credential stuffing. By requiring a second factor, it considerably limits the direct exploitation of a compromised password. However, its effectiveness depends heavily on how it is implemented. Several points determine the real effectiveness of multifactor authentication

• the type of second factor used
• the exemptions granted (trusted devices, long sessions)
• the real coverage of the account base
• the handling of recovery procedures

A second factor based on codes sent by SMS, for example, remains exposed to fraud or hijacking scenarios. Likewise, multifactor authentication that is optional or limited to certain categories of users leaves a significant attack surface. And above all, multifactor authentication does not eliminate credential stuffing, it only mitigates its consequences.

Cross-Referencing Indicators to Detect Better

Traditional defence mechanisms are often designed to spot abnormal volumes of failed logins. Yet in credential stuffing, attackers adjust their attacks to stay under these thresholds. A more effective approach is therefore to shift the focus to authentication behaviours, rather than to the number of failures alone.

Several weak signals, taken in isolation, can reveal a campaign in progress

• a multiplication of attempts across a large number of distinct accounts
• inconsistencies between the geographic distribution of attempts and that of the known user population
• unusual variations in the technical environments used
• an abnormal success rate followed by atypical activity

Taken separately, each of these indicators may seem harmless; once added together, and analyzed together and over time, they make it possible to identify the patterns characteristic of credential stuffing. This approach, however, requires a finer capacity for correlation and behavioural analysis (and therefore more sustained technical and financial resources) than simple blocking mechanisms after repeated failures.

Building Leak Data into Risk Management

An organization does not control the leaks that happen elsewhere. It can, however, build this reality into its own defence strategy. Continuous monitoring of compromised databases available publicly or through specialized partners makes it possible to identify potential exposures before attacks happen. When an address associated with an internal account appears in a leak, the risk of credential stuffing mechanically increases.

The Specific Question of Privileged Accounts

Not all accounts have the same value. Privileged accounts are particularly attractive targets in credential stuffing campaigns, especially when they use addresses and passwords that are also used for personal purposes. Credential stuffing exploits the cross-cutting nature of digital habits. The more varied the environments an account is exposed to, the greater the probability that it appears in a leak. These accounts must therefore be audited regularly, and granted only when they are indispensable and preferably for a limited period.

Security policies that ignore users' real practices leave structural vulnerabilities in place. Credential reuse, informal account sharing, a proliferation of unlisted tools: these practices widen the attack surface well beyond the theoretical perimeter. The response therefore also involves better control of real digital habits, rather than hoping users will be more disciplined than they really are. Credential stuffing is a reminder that security must also rest on a detailed understanding of how people actually use systems. Join us again soon on the blog for a new topic. If you have a film, a series, software or an ebook to protect, don't hesitate to call on our services by contacting one of our account managers; PDN has been a pioneer in cybersecurity and anti-piracy for more than ten years, and we certainly have a solution to help you. Happy reading, and see you soon!

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