Unveiling a Critical Threat: Exploiting Microsoft Access "Linked Table" for NTLM Forced Authentication Attacks

3 min read
Unveiling a Critical Threat: Exploiting Microsoft Access "Linked Table" for NTLM Forced Authentication Attacks


In a recent cybersecurity revelation, a critical vulnerability has come to light, posing a substantial risk to users of Microsoft Access. This exploit has the potential to execute NTLM forced authentication attacks, putting user credentials at risk and potentially leading to unauthorized access to sensitive data.

Impact Analysis

The gravity of this vulnerability lies in its capacity to enable attackers to surreptitiously extract Windows user NTLM tokens. These tokens are then transmitted to a server controlled by the attacker, leveraging any TCP port, including widely used port 80. The consequences are severe, granting attackers the ability to misuse these credentials for impersonation or to perpetrate further malicious activities.

This vulnerability allows for automatic leakage of NTLM tokens, a cryptographic authentication protocol used by Windows, during the process of opening a malicious Microsoft Access database. The transmitted tokens can subsequently be exploited for various cyber threats, posing a multifaceted risk to user security.

How the Attack Works

The modus operandi of this attack revolves around exploiting the Microsoft Access "Linked Table" feature. Initially designed to facilitate connectivity with external data sources, such as SQL Server databases, this feature unwittingly becomes a conduit for attackers. By crafting a malevolent Access database housing a linked table pointing to a server controlled by the attacker, the assailant can discreetly capture the user's NTLM token when the victim unsuspectingly opens the compromised database.

Technical Insights

In-depth analysis reveals that the NTLM forced authentication attack capitalizes on the inherent functionality of the "Linked Table" feature, manipulating it to exfiltrate sensitive information. The intricate technical details highlight the need for a comprehensive understanding of the vulnerability to effectively counteract potential exploits.

Security Mitigation

  1. Patch Application Microsoft has responded swiftly to this emerging threat by releasing a dedicated patch. It is imperative for users to promptly install the patch, reinforcing their systems against potential vulnerabilities. Regular monitoring of Microsoft's security updates is crucial to stay abreast of evolving threats.
  2. Disable Linked Table Feature As an additional layer of defense, users can opt to disable the "Linked Table" feature in Microsoft Access. This can be accomplished by navigating to the Microsoft Access Options dialog box, selecting the Current Database tab, and, in the Linked Table Manager section, checking the "Disable all linked tables" option.

Further research indicates that configuring firewalls and intrusion detection systems to scrutinize and block suspicious outbound traffic may provide an added layer of protection. Collaborating with IT security professionals to assess and enhance overall cybersecurity posture is recommended.


The severity of this vulnerability underscores the urgency of fortifying Microsoft Access environments. Users must exercise heightened vigilance by promptly applying patches, disabling vulnerable features, and implementing supplementary security measures. In an era of evolving cyber threats, proactive engagement and a multi-faceted approach to cybersecurity are paramount to ensuring the resilience of digital ecosystems against sophisticated attacks.

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