CVE-2026-21511: Microsoft Outlook Spoofing Vulnerability
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
Other sources
Microsoft Outlook Spoofing Vulnerability
— Microsoft
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 16.0.10417.20097Patch KB5002836 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in https://aka.ms/OfficeSecurityReleases - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 16.0.5539.1002Patch KB5002840 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 16.0.5539.1002Patch KB5002839 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 16.106.26020821 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 16.0.19127.20518Patch KB5002833
Event History
Frequently Asked Questions
What is the severity of CVE-2026-21511?
CVE-2026-21511 is classified as a medium severity vulnerability due to its potential to allow spoofing attacks.
How do I fix CVE-2026-21511?
To fix CVE-2026-21511, ensure that you apply the latest security updates provided by Microsoft for the affected products.
Which products are affected by CVE-2026-21511?
CVE-2026-21511 affects multiple Microsoft Office products including Outlook, Word, and SharePoint Server across various editions.
Can CVE-2026-21511 be exploited remotely?
Yes, CVE-2026-21511 can be exploited by an unauthorized attacker over the network to perform spoofing.
What type of vulnerability is CVE-2026-21511?
CVE-2026-21511 is a spoofing vulnerability caused by the deserialization of untrusted data in Microsoft Office Outlook.