What is CVE-2026-55008?

CVE-2026-55008 is a critical-severity vulnerability in Microsoft Exchange Server 2016 Cumulative Update 23, classified under Cross-site Scripting. CVSS score: 9.6/10. Published 2026-07-14.

How severe is CVE-2026-55008?

Critical severity. CVSS v3 base score is 9.6 out of 10.

XSS in Microsoft Exchange Server 2016 Cumulative Update 23

CVE-2026-55008

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

Vulnerability class: XSS (Cross-Site Scripting)

CVSS v3 metric

CVSS v3 base score 9.6 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H.

Affected products

Microsoft Exchange Server 2016 Cumulative Update 23 — versions 15.01.0.0
Microsoft Exchange Server 2019 Cumulative Update 14 — versions 15.02.0.0
Microsoft Exchange Server 2019 Cumulative Update 15 — versions 15.02.0.0
Microsoft Exchange Server Subscription Edition Rtm — versions 15.02.0.0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

secure@microsoft.com (vendor-advisory, patch)

Frequently asked questions

What is CVE-2026-55008?: CVE-2026-55008 is a critical-severity vulnerability in Microsoft Exchange Server 2016 Cumulative Update 23, classified under Cross-site Scripting. CVSS score: 9.6/10. Published 2026-07-14.
How severe is CVE-2026-55008?: Critical severity. CVSS v3 base score is 9.6 out of 10.