What is CVE-2017-8621?

CVE-2017-8621 is a medium-severity vulnerability in Microsoft Exchange Server, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2017-07-11.

How severe is CVE-2017-8621?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Open Redirect in Microsoft Exchange Server

CVE-2017-8621

Microsoft Exchange Server 2010 SP3, Exchange Server 2013 SP3, Exchange Server 2013 CU16, and Exchange Server 2016 CU5 allows an open redirect vulnerability that could lead to spoofing, aka "Microsoft Exchange Open Redirect Vulnerability".

Vulnerability class: Open Redirect

Published 2017-07-11 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.032 (87.6th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 88th percentile — 87.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.032 · newest: 0.032 · change: 0.000

Affected products

Microsoft Exchange Server — versions 2010, 2013, 2016
Microsoft Corporation Exchange Server 2010 Sp3, 2013 Cu16, And 2016 Cu5. — versions Microsoft Exchange

Weakness classification (CWE)

CWE-601 — URL Redirection to Untrusted Site (Open Redirect)

References

portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2017-8621 (Patch, Vendor Advisory)
www.securitytracker.com/id/1038852 (VDB Entry, Third Party Advisory, vdb-entry)
www.securityfocus.com/bid/99533 (VDB Entry, Third Party Advisory, vdb-entry)

Frequently asked questions

What is CVE-2017-8621?: CVE-2017-8621 is a medium-severity vulnerability in Microsoft Exchange Server, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2017-07-11.
How severe is CVE-2017-8621?: Medium severity. CVSS v3 base score is 6.1 out of 10.