When a data breach is revealed, it is generally treated as a one-off event. When a database is compromised, an official statement and recommendations are issued, and then the company or institution often moves on to another, more pressing issue. However, these leaks continue to have an impact long after the event. They constitute a lasting stock of data that can be exploited and is exploited for years by cybercriminals. This exploitation of old data is known as “credential stuffing.”
This first part aims to understand why credentials stolen sometimes more than ten years ago remain fully exploitable today, and how this reality fuels a form of hacking that has become structural. The second part of our article will focus on effective responses to adopt when such an attack is discovered.
Credential stuffing involves automatically testing credentials that have already been compromised on other services. Unlike brute force attacks or the exploitation of technical vulnerabilities, it does not involve forcing access, but rather reusing existing access.
This technique relies on a behavior that is widespread among the vast majority of users: reusing the same credentials on multiple platforms. An email address/password combination created for a secondary service can thus become, years later, a gateway to much more sensitive services.
In practice, a credential stuffing attack follows a relatively stable logic
From the perspective of the targeted systems, these connections appear legitimate. The username is valid, as is the password. No conventional security mechanisms are therefore circumvented.
The idea that an old leak is obsolete is misleading. In reality, old databases are a particularly valuable source of raw material for attackers.
They are easy to obtain, inexpensive, and allow attackers to identify patterns that help them map user behavior.
Even when passwords have been changed, this data remains valuable. It reveals habits: recurring structures, lexical preferences, patterns of variation. On a large scale, these elements make it possible to optimize attempts and significantly increase success rates.
Credential stuffing therefore seeks above all to identify all digital environments in which individuals whose data has been compromised still have an active account.
Unlike other forms of hacking, credential stuffing does not diminish over time. It actually grows stronger.
As the years go by, the more accounts a single user accumulates, the more digital services multiply, and the more the attack surface for the hackers expands.
A leak that occurred several years ago can now provide access to services that did not even exist at the time of the initial compromise. The attacker is not interested in the origin of the leak, but in what still works.
This dynamic explains why old databases continue to be actively used, sometimes much more than recent leaks, in current hacking campaigns.
Credential stuffing is now an industrialized activity. Attacks are automated, and designed to blend in with normal traffic.
Attackers constantly adjust their parameters
distribution of attempts over time:
The goal is not to cause a detectable spike, but to maintain constant, discreet pressure. Hacking no longer takes the form of a sudden incident, but rather a constant background noise, making it much more difficult to identify and isolate.
This industrialization creates a strong asymmetry. The cost of an attempt is virtually non-existent for the attacker, while each successful compromise can have dramatic consequences for the targeted organization.
Credential stuffing can therefore be used for:
In a professional setting, a single account can be enough to access collaborative tools, view internal documents, or prepare larger attacks, without ever triggering an immediate alert.
For platforms, the impact is also reputational. It doesn’t matter if the initial leak came from another service. In the eyes of users, it is the service on which the account was compromised that is held responsible.
Many organizations believe they are protected because
These measures are obviously necessary, but they do not address the core of the problem. As we have seen, credential stuffing uses valid credentials. It therefore does not trigger any obvious technical alerts or manifestly abnormal behavior.
Attackers adapt their attacks to remain below detection thresholds. As a result, the crisis is not visible and is often discovered far too late.
Credential stuffing is not a passing trend. It is the direct result of how digital practices have developed over the years: proliferation of services, dependence on passwords, historical accumulation of leaks, poor overall digital hygiene. As long as these conditions persist, old leaks will continue to fuel current attacks. Their age does not neutralize them. It makes them exploitable in the long term. Join us in mid-February to explore solutions for limiting the consequences of credential stuffing. In the meantime, if you have a movie, TV series, software, or e-book 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 over ten years, and we are sure to have a solution to help you. Happy reading, and see you soon!
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