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.

Published: 2026-02-10 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21511 is rated Moderate Risk (64/100): CVSS High severity, with medium exploitation likelihood (EPSS 3.64%). EPSS rose +3.21% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21511

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.42% 3.64% +3.21%
2 2026-06-12 0.35% 0.42% +0.07%
3 2026-05-13 — 0.35% —

Full EPSS history (7 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21511

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-21511

Affected software / configurations for CVE-2026-21511

Vendor Product Version Raw CPE
microsoft 365_apps — cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
microsoft 365_apps — cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
microsoft office 2019 cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
microsoft office 2019 cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
microsoft office_long_term_servicing_channel 2021 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x64:*
microsoft office_long_term_servicing_channel 2021 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*
microsoft office_long_term_servicing_channel 2021 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:macos:*:*
microsoft office_long_term_servicing_channel 2024 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*
microsoft office_long_term_servicing_channel 2024 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*
microsoft office_long_term_servicing_channel 2024 cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:macos:*:*
microsoft sharepoint_server < 16.0.19127.20518 cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*
microsoft sharepoint_server 2016 cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*
microsoft sharepoint_server 2019 cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*
microsoft word 2016 cpe:2.3:a:microsoft:word:2016:*:*:*:*:*:x64:*
microsoft word 2016 cpe:2.3:a:microsoft:word:2016:*:*:*:*:*:x86:*

References for CVE-2026-21511

cvelogic Threat Intelligence