Outlook
CVE-2026-21511
HIGH
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Lifecycle Timeline
2DescriptionCVE.org
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. No patch is currently available, making this a high-risk threat requiring immediate defensive measures.
Technical ContextAI
Classified as CWE-502 (Deserialization of Untrusted Data). Affects 365 Apps. Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
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Same weakness CWE-502 – Deserialization of Untrusted Data
View allSame technique Deserialization
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External POC / Exploit Code
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