CVE-2024-43451: Microsoft Windows NTLMv2 Hash Disclosure Spoofing Vulnerability

CVE-2024-43451 is a spoofing vulnerability in Microsoft Windows that can disclose a user's NTLMv2 hash when a file is opened. An attacker who obtains that hash may then use it to impersonate the affected user.

This class of issue matters in Windows environments because NTLM authentication material, once captured, can support unauthorized access or further activity if the environment still relies on NTLM. Public detail is limited to the CISA description; confirm exact impact and scope against the vendor advisory.

How it works

The weakness is catalogued as CWE-73 (External Control of File Name or Path). According to the available summary, Microsoft Windows contains an NTLMv2 hash spoofing vulnerability that can result in disclosing a user's NTLMv2 hash to an attacker via a file open operation. The attacker could then leverage this hash to impersonate that user.

In practical terms for defenders, the flaw involves a path or file-related operation that triggers an NTLM authentication exchange under attacker influence, allowing the hash to leave the system. No further exploit mechanics, required conditions, or payload details are provided in the source facts; treat any additional claims as unconfirmed and verify them only against the official Microsoft advisory.

Am I affected? How to find it in your systems

The vulnerability affects Microsoft Windows. It can appear on any system that processes file open operations in a way that can initiate NTLM authentication, which is common on domain-joined workstations, servers, and file-sharing hosts.

• Inventory all Windows endpoints and servers (workstations, member servers, domain controllers) using your existing asset management, SCCM/Intune, or vulnerability scanners.
• Identify systems that still permit NTLM authentication or that routinely open files from untrusted or remote locations (network shares, email attachments, web downloads).
• Confirm exact affected builds and configurations only against the vendor advisory; do not rely on version lists that are not present in the source facts.
• For detection of possible exploitation, review authentication logs (Security event logs for NTLM logon events), SMB or file-access telemetry, and any network captures showing unexpected outbound NTLM challenges. Look for anomalous file-open activity that coincides with NTLM traffic to unexpected destinations. Absence of such signs does not prove safety; the source facts do not document specific indicators of compromise.

How to remediate

Apply the mitigations or updates provided by Microsoft as the primary remediation. The CISA required action is to apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

• Deploy the vendor-supplied security update through your standard patch management process as soon as it is validated in your environment.
• After patching, re-verify that NTLM-related configurations remain hardened (for example, preferring Kerberos, restricting NTLM where policy allows) according to Microsoft guidance.
• Validate remediation by confirming the update is installed and by re-testing any file-open or authentication paths that previously triggered the issue, again using only methods described in the vendor advisory.

If you can't patch immediately

Until the vendor update can be applied, reduce exposure with compensating controls appropriate to NTLM hash disclosure and path-control weaknesses.

• Segment networks so that systems handling untrusted files cannot freely initiate NTLM authentication to untrusted or external hosts.
• Where operationally feasible, restrict or disable NTLM authentication in favor of Kerberos, or apply group-policy restrictions on outbound NTLM, confirming the exact settings against Microsoft documentation.
• Limit the ability of users or processes to open files from untrusted sources (email, web, removable media, or untrusted shares) through application control, attachment filtering, or least-privilege file-access policies.
• Increase monitoring for NTLM authentication events and unexpected SMB or file-open activity; alert on anomalies and retain logs for investigation.
• Consider virtual patching or network-level filtering only if it can be shown to block the relevant file-open or authentication path without inventing unstated signatures; validate any such control against the vendor advisory.

If your data may have been exposed

Actively exploited vulnerabilities of this type can lead to credential compromise and subsequent unauthorized access. The source facts do not document known ransomware use. If you suspect NTLMv2 hashes or related credentials may have been obtained, treat the accounts as potentially compromised: reset passwords or rotate credentials, review authentication logs for misuse, and follow your incident-response process. You can also run a free exposure scan of your email addresses against known breach data to check whether related accounts appear in public breach collections.