Credential disclosure via outbound NTLM authentication
Published Feb 10, 2026 · Updated Feb 10, 2026
Information disclosure in Microsoft Outlook and affected Office and SharePoint releases allows remote attackers to obtain NTLM credentials. A specially crafted email causes Outlook preview processing to initiate outbound NTLM authentication to an attacker-controlled server, exposing credential material. No authentication or message opening is required because the Preview Pane is an attack vector; the reported consequence is credential disclosure rather than data modification or service interruption.
Summary
What happened
Information disclosure in Microsoft Outlook and affected Office and SharePoint releases allows remote attackers to obtain NTLM credentials. A specially crafted email causes Outlook preview processing to initiate outbound NTLM authentication to an attacker-controlled server, exposing credential material. No authentication or message opening is required because the Preview Pane is an attack vector; the reported consequence is credential disclosure rather than data modification or service interruption.
The record
- CVE
- CVE-2026-21260
- Published
- Feb 10, 2026
- Updated
- Feb 10, 2026
- Vendor
- Microsoft
- Product
- Microsoft Office 2019
- Classifications
- CWE-200, T1187
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 10, 2026CVE publishedPublication date reported by the CVE source.
- Feb 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=19.0.0 <https://aka.ms/OfficeSecurityReleases
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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