Hi@all,

VMWare Zimbra Mailer Release 8.6.0.GA, latest patch and prior versions 
with DKIM implementation are vulnerable to longterm Mail Replay attacks.

If the expiration header is not set, the signature never expires. This 
means, that the e-mail, perhaps catched while performing a man in the 
middle attack, can be replayed years after catching it.

This can be combined with the spoofed reply-to header field, because the 
header field is not hashed by Zimbras DKIM implementation.

Supporter of vulnerability analysis: Steffen Mauer @this point I want to 
thank Steffen for his good work =)

Background:
To configure DKIM with VMware Zimbra the official documentation advises 
the administrator to use  the zimbra management tools. With the 
management tools there is no possibility to add custom Header’s for 
hashing it with DKIM or for setting the expiration DKIM Header. 
(https://wiki.zimbra.com/wiki/Configuring_for_DKIM_Signing)

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PoC Headerpart:
The DKIM Implementation implements the following DKIM Header:
Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=0mail.org; 
s=76820800-C732-11E5-858E-A0DD11F66BE4; t=1454147943; 
bh=c/tw0mGbL980zPjwnIKgPM7ubA7wLOVGbMr3y9WADOY=; 
h=From:Content-Type:Content-Transfer-Encoding:Subject:Message-Id: 
Date:To:Mime-Version; 
b=c8dL4dRpnjMeV2OxFbz+1Z2n49PDlUx+XsiodKvmAOh1znOxRW3NDKYk7Bwmlw453 
04uFAwLsBl7M1u7mxr/wdp4fZTEQtfJhhUonNJMKDBOxTdiQPOLhcVKC2tEaSLyKpq 
Rvtp9ECFFqHstyRHk57UOzMi8PMRusl8lP5B43kY=
________________________________________
Report Timeline:

There has been no response from VMware for 14 Days.


Best regards / Mit freundlichen Grüßen

Tim Schughart
IT Security engineer

ProSec Networks
Website: https://www.prosec-networks.com
E-Mail: info@prosec.networks.com
Phone: +49(0) 2621 9469 252