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Category:   Application (E-mail Server)  >   Exim Vendors:   Exim.org
Exim Use-After-Free Memory Error in SMTP Service Lets Remote Users Execute Arbitrary Code on the Target System
SecurityTracker Alert ID:  1039872
SecurityTracker URL:  http://securitytracker.com/id/1039872
CVE Reference:   CVE-2017-16943   (Links to External Site)
Date:  Nov 27 2017
Impact:   Execution of arbitrary code via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 4.88 - 4.89
Description:   A vulnerability was reported in Exim. A remote user can execute arbitrary code on the target system.

A remote user can connect to the SMTP service and send a specially crafted BDAT command to trigger a use-after-free memory error in the ESMTP CHUNKING extension and execute arbitrary code on the target system. The code will run with the privileges of the target service.

meh reported this vulnerability.

Impact:   A remote user can execute arbitrary code on the target system.
Solution:   The vendor has issued a source code fix, available at:

https://git.exim.org/exim.git/commitdiff/4e6ae6235c68de243b1c2419027472d7659aa2b4

The vendor has described a workaround:

".. in the main section of your Exim configuration, set:

chunking_advertise_hosts =

This disables advertising the ESMTP CHUNKING extension, making the BDAT verb unavailable and avoids letting an attacker apply the logic."

The vendor plans to include a fix in future version 4.90.

Vendor URL:  bugs.exim.org/show_bug.cgi?id=2199 (Links to External Site)
Cause:   Access control error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Nov 27 2017 (Ubuntu Issues Fix) Exim Use-After-Free Memory Error in SMTP Service Lets Remote Users Execute Arbitrary Code on the Target System
Ubuntu has issued a fix for Ubuntu Linux 17.04 and 17.10.



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