Regression Bug: Windows Update KB5065426 breaks legacy Microsoft.Jet.OLEDB.4.0 connectivity with 'Not a valid password' error

A significant behavioral regression has been introduced by the recent security update KB5065426 (OS Build 26100.6584), impacting applications that rely on the legacy Microsoft.Jet.OLEDB.4.0 provider to connect to either password-protected or non-password-protected Access databases. Immediately following the installation of this patch, database connection attempts fail with an unhandled "Not a valid password" exception, despite the credentials being accurate.

This behavior is actively disrupting environments globally, as documented across several community channels:

• Microsoft Q&A Portal (Thread #5602291)
• Microsoft Q&A Portal (Thread #5567210)

While the enterprise community fully acknowledges that Microsoft.Jet.OLEDB.4.0 is a legacy data provider, and that upgrading to the modern Microsoft.ACE.OLEDB library is the established strategic path forward, the nature of this failure warrants engineering intervention rather than a standard deprecation dismissal.

If a legacy component is truly frozen and unsupported, routine cumulative security patches should technically leave its internal execution paths untouched. The fact that KB5065426 immediately induced this password validation failure proves that the patch modified underlying OS dependencies, cryptographic handling, or memory validation routines utilized by the Jet provider.

Consequently, this is an unintended functional regression introduced by a security update that not a request for a new enhancement, nor an appeal to patch a long-standing legacy bug. Had this specific security update not destabilized the component, these legacy production systems would continue to operate reliably without unexpected downtime.

Currently, administrators are forced into an unacceptable trade-off: either uninstall critical security patch KB5065426 to restore business-critical application functionality, or leave systems vulnerable to retain operational status.

We request that the Windows servicing and Data Access engineering teams investigate the specific changes KB5065426 introduces to legacy authentication and string-handling libraries (such as vbajet32.dll), and issue a cumulative hotfix to preserve backward compatibility for organizations managing these transitions.