Zimbra Collaboration Suite Cross Site Scripting

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# COMPASS SECURITY ADVISORY https://www.compass-security.com
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# COMPASS SECURITY ADVISORY https://www.compass-security.com
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# CVE ID : CVE-2017-8802
# Product: Zimbra Collaboration Suite (ZCS) [1]
# Vendor: Synacor Inc. [2]
# Subject: Stored Cross-Site Scripting (XSS) Vulnerability
# Risk: High
# Effect: Exploitable by Anonymous Internet Adversaries
# Triggered in the Context of an Authenticated Zimbra Email User
# Authors: Damian Pfammatter (damian.pfammatter@compass-security.com)
# Alessandro Zala (alessandro.zala@compass-security.com)
# Date: January 10th 2018
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Introduction:
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The Zimbra Collaboration Suite (ZCS) is a collaborative software suite that includes Email servers
as well as Email clients. According to the product website, more than 500 million people are
currently using the Email collaboration tool [1].

Security Analysts of Compass Security Schweiz AG [3] discovered a Stored Cross-Site Scripting (XSS)
vulnerability in the Zimbra Email web client, potentially resulting in a number of different attack
scenarios.


Affected Versions:
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No confirmed information about all affected versions is available. Versions prior to 8.8 GA Release
are likely affected.


Technical Description:
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The Zimbra Email web client is affected by a Stored Cross-Site Scripting (XSS) vulnerability.

Remote attackers can target the vulnerability by sending an Email with XSS payload (e.g. JavaScript)
in its body. In case the recipient selects the email in the Zimbra client, and accesses the "Show
Snippet" functionality using the "Q" shortcut, the XSS payload is executed in the context of the
recipient's Zimbra client.

For example through social engineering, attackers could bring their victims into pressing "Q" while
reading the compromised email, triggering the payload. Beside others, the malicious payload could
compromise the confidentility, integrity as well as availability of the victim's emails. Also it
could be possible to change Zimbra settings of the corresponding victim.


Hotfix:
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The corresponding patch has been released in version 8.8.0 Beta2 [4] (Bug #107925). The patch is
part of public release 8.8 GA Release.


Timeline:
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2017-05-04: Vulnerability discovered
2017-05-05: Initial vendor notification
2017-05-05: Vendor confirmed security issue
2017-05-05: MITRE reserved CVE-2017-8802 for the issue
2017-12-12: Vendor released security fix & guidance to its customers
2018-01-10: Public disclosure


References:
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[1] https://www.zimbra.com/
[2] https://www.synacor.com/
[3] https://www.compass-security.com/research/advisories/
[4] https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories