7.5

CVE-2026-21511: microsoft 365_apps Deserialization of Untrusted Data

CVSS: 7.5v3.1HighAnalyzed
Published 10-02-2026Last modified 19-08-2026
Open JSON

Vulnerability summary

CVE-2026-21511 is a high (CVSS 7.5) Deserialization of Untrusted Data vulnerability in microsoft 365_apps. EPSS estimates a 3.97% chance of exploitation in the next 30 days, higher than 90.4% of scored vulnerabilities.

Overall risk
31/100
0100
Medium · default modelHow is this calculated?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
3.97%
0%100%
Low · +0.20 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 10-02-2026
    PublishedVulnerability first disclosed.
  2. 19-08-2026
    Last modifiedVulnerability information updated.

Description

Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

CVSS metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

3.97%

Chance of exploitation in the next 30 days

Percentile

90%

Versus all other CVEs

30-day change

+0.20 pp

From 3.77% on 21-09-2026

21-09-202621-10-2026
EPSS score
3.97%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Microsoft15 products

1 vendor · 15 products

References

1 links