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CVE-2018-20160

30
FAUCET Score

CVE-2018-20160 describes an XML External Entity (XXE) vulnerability in ZxChat, used in Synacor Zimbra Collaboration Suite versions 8.7 and 8.8, allowing attackers to submit crafted XML requests to the mailboxd service. This critical vulnerability, with a CVSS score of 9.8, requires no user interaction or authentication, enabling full compromise of confidentiality, integrity, and availability. Despite its high severity, there is no evidence of active exploitation, publicly available exploit code, or significant community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
>= 8.7.0, < 8.7.11CPE matchmatch criteria
cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*
>= 8.8.0, < 8.8.9CPE matchmatch criteria
cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*
8.7.11CPE matchmatch criteria
cpe:2.3:a:synacor:zimbra_collaboration_suite:8.7.11:-:*:*:*:*:*:*
8.7.11CPE matchmatch criteria
cpe:2.3:a:synacor:zimbra_collaboration_suite:8.7.11:p1:*:*:*:*:*:*
8.7.11CPE matchmatch criteria
cpe:2.3:a:synacor:zimbra_collaboration_suite:8.7.11:p2:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

9.8CRITICAL

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.0

Exploit Intelligence

EPSS Score
2.23%
Probability of exploitation in next 30 days
EPSS Percentile
80.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0223 is in the 70th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

bugzilla.zimbra.com / show_bug.cgi
Issue TrackingThird Party Advisory
wiki.zimbra.com / wiki/Security_Center
Release NotesVendor Advisory
wiki.zimbra.com / wiki/Zimbra_Security_Advisories
Vendor Advisory