Why valid logins are becoming a cybersecurity risk

A successful login is no longer proof that the person behind it is legitimate. Attackers increasingly use stolen credentials, authentication tokens and hijacked sessions to enter through the front door, then move through corporate systems as if they were authorized employees, according to TechRadar.

In 2026, hackers breached systems used by the UK Foreign Office and local councils with stolen login credentials, the report says. The UK’s Cyber Security Breaches Survey 2025 found that phishing affected 85% of businesses that experienced a breach or attack, making it the most common cyber threat in that group.

Why authentication is no longer enough

Traditional security treats authentication as a decisive event: a user enters the correct password, completes a multi-factor authentication challenge and receives access. But phishing, infostealer malware, session hijacking and credential harvesting have made valid account access easier to obtain.

Authentication confirms only that the correct credentials were presented at a particular moment. It does not establish that the same person remains behind the keyboard, or that the user’s behavior remains safe after access is granted. Compromised credentials and tokens are also traded on dark-web forums, giving attackers ready-made access to trusted environments.

The alternative is a continuous-trust model rooted in Zero Trust. Every request, transaction and interaction is evaluated against the user’s expected identity and context. An account that normally connects from a familiar location during working hours might initially be low risk; if it suddenly accesses unfamiliar systems or deviates from its established patterns, its trust level should fall automatically.

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Behavioral signals can expose impersonation

Users create a digital behavioral fingerprint through the applications they access, the datasets they handle, their working hours and their normal workflows. Machine learning and other analytics can assess those signals in real time, identifying when activity no longer matches the established baseline.

That matters because attackers with legitimate credentials may deliberately move slowly and mimic normal operations. Behavioral analysis can add scrutiny where conventional intrusion detection—and static indicators of compromise that quickly become outdated—may miss impersonation.

Identity security also affects business continuity. Modern organizations connect employees, contractors, partners, suppliers and customers across multiple systems, so one compromised identity can become a route into several services. The report argues that defenses should limit unnecessary privileges, continuously validate access rights, reduce identity sprawl and maintain visibility across the full identity ecosystem.

The practical shift is straightforward: authentication should begin a security assessment, not end it. Trust must be dynamic, measurable and repeatedly verified as identities, permissions and behavior change.

Update, 17 September 2026 — Microsoft confirms domain-login failure

The Register reports that Microsoft added a known issue on September 16 affecting Windows 11 24H2, 25H2 and 26H1 after the September 2026 security update, KB5124008. Credential Guard-protected machine accounts can lose their secure channel to an on-premises Active Directory domain, leaving users unable to sign in even with valid domain credentials.

Microsoft said the problem occurs where Machine Identity Isolation enforcement had already been configured but devices are not connected to domain controllers at the Windows Server 2025 Domain Functional Level or later. Administrators must disable the feature through the method used to enable it, restart affected devices and repair the secure channel with the Test-ComputerSecureChannel PowerShell command. Microsoft said a future update will temporarily prevent enforcement while it changes the feature.