CVE-2026-21511
Microsoft Outlook Spoofing Vulnerability
No known exploitation. EPSS puts it in the 90th percentile. A vendor fix is available.
What to do
The vendor has published a fix. Version details are below where the sources state them.
What it is
From the CVE record
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
3.8% chance of exploitation activity in the next 30 days, which ranks it in the 90th percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
6 events over 135 days, from the signal feeds we watch.
- OpenVAS check added
- Patch availablerecord updated
- Publishedweakness classified, att&ck mapped
Affected products
- Microsoft Office LTSC 2021Consumer Software / productivity
- Microsoft 365 Apps for EnterpriseConsumer Software / productivity
- Microsoft SharePoint Server Subscription EditionEnterprise Software / document-mgmt
- Microsoft SharePoint Server 2019Enterprise Software / document-mgmt
- Microsoft SharePoint Enterprise Server 2016Enterprise Software / document-mgmt
- Microsoft Word 2016Consumer Software / productivity
- Microsoft Office LTSC for Mac 2021Consumer Software / productivity
- Microsoft Office LTSC for Mac 2024Consumer Software / productivity
And 15 more affected products. See all after sign-in
Technical detail
CVSS 3.1 vector
Open in the CVSS calculatorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Scored 7.5 by NVD.
How it is reached
- Attack Vector NetworkExploitable remotely over the network without any special conditions
- Attack Complexity LowNo special conditions — the attack can be reliably reproduced
- Privileges Required NoneNo authentication required — anyone can exploit this
- User Interaction NoneNo user interaction needed — fully automated exploitation
Scope
- Scope UnchangedImpact is limited to the vulnerable component itself
Impact if exploited
- Confidentiality HighTotal information disclosure — all data in the component is compromised
- Integrity NoneNo integrity impact
- Availability NoneNo availability impact
Weaknesses
ATT&CK techniques
Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.
Sources
References in the record
In the news
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