Bug 1517680 (CVE-2017-16943)

Summary:	CVE-2017-16943 exim: use-after-free in receive_msg function via vectors involving BDAT commands
Product:	[Other] Security Response	Reporter:	Adam Mariš <amaris>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	urgent	Docs Contact:
Priority:	urgent
Version:	unspecified	CC:	bennie.joubert, dwmw2, jskarvad, tremble
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-11-27 09:02:33 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1517686, 1517687
Bug Blocks:

Description Adam Mariš 2017-11-27 08:47:06 UTC

The receive_msg function in receive.c in the SMTP daemon in Exim 4.88 and 4.89 allows remote attackers to execute arbitrary code or cause a denial of service (use-after-free) via vectors involving BDAT commands.

Upstream bug:

https://bugs.exim.org/show_bug.cgi?id=2199

Upstream patch:

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

Comment 1 Adam Mariš 2017-11-27 08:54:14 UTC

Created exim tracking bugs for this issue:

Affects: epel-all [bug 1517686]
Affects: fedora-all [bug 1517687]

Comment 2 Adam Mariš 2017-11-27 08:56:38 UTC

Mitigation:

if you are running Exim 4.88 or newer, then 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.