What is CVE-2018-20160?

CVE-2018-20160 is a critical-severity vulnerability in Synacor Zimbra Collaboration Suite, classified under Improper Restriction of XML External Entity Reference (XXE). CVSS score: 9.8/10. Published 2019-05-29.

How severe is CVE-2018-20160?

Critical severity. CVSS v3 base score is 9.8 out of 10.

XXE in Synacor Zimbra Collaboration Suite

CVE-2018-20160

ZxChat (aka ZeXtras Chat), as used for zimbra-chat and zimbra-talk in Synacor Zimbra Collaboration Suite 8.7 and 8.8 and in other products, allows XXE attacks, as demonstrated by a crafted XML request to mailboxd.

Vulnerability class: XXE (XML External Entity)

Published 2019-05-29 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.022 (82.2th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 82nd percentile — 82.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.022 · newest: 0.022 · change: 0.000

Affected products

Synacor Zimbra Collaboration Suite — versions 8.7.11, 8.8.9, 8.8.10

Weakness classification (CWE)

CWE-611 — Improper Restriction of XML External Entity Reference (XXE)

References

wiki.zimbra.com/wiki/Zimbra_Security_Advisories (Vendor Advisory)
wiki.zimbra.com/wiki/Security_Center (Release Notes, Vendor Advisory)
bugzilla.zimbra.com/show_bug.cgi (Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2018-20160?: CVE-2018-20160 is a critical-severity vulnerability in Synacor Zimbra Collaboration Suite, classified under Improper Restriction of XML External Entity Reference (XXE). CVSS score: 9.8/10. Published 2019-05-29.
How severe is CVE-2018-20160?: Critical severity. CVSS v3 base score is 9.8 out of 10.