Outlook CVE-2026-21511
HIGHCVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Lifecycle Timeline
2DescriptionNVD
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
AnalysisAI
Microsoft Outlook's unsafe deserialization of untrusted data enables remote attackers to spoof messages and identities without authentication over the network. This vulnerability affects Outlook, Word, and Microsoft 365 Apps, allowing attackers to impersonate legitimate senders and deceive users. …
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RemediationAI
Within 24 hours: Identify all Outlook deployments and users, assess email traffic for suspicious deserialization patterns, and notify security teams to monitor for active exploitation. Within 7 days: Implement email gateway filtering rules to block malicious serialized objects, restrict Outlook's ability to process untrusted file attachments, and disable legacy protocols if not business-critical. …
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