Bug 1942581

Summary:	exim: CNAME handling can break TLS certificate verification
Product:	[Other] Security Response	Reporter:	Michael Kaplan <mkaplan>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED UPSTREAM	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	bennie.joubert, dwmw2, jskarvad
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:	2021-03-24 17:35:18 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:	1942582, 1942583
Bug Blocks:

Description Michael Kaplan 2021-03-24 14:56:19 UTC

When Exim is configured to verify certificates against hostnames and hostname
resolution yields a CNAME, then Exim will verify the certificate against the
canonical name rather than the original hostname.

An attacker with control over the network (e.g. a rogue public wifi) can forge
CNAME records to point to a hostname under their control.  They can then
obtain a legitimate certificate for the host under their control, which Exim
will accept as valid for the host it intended to connect to.

Comment 1 Michael Kaplan 2021-03-24 14:56:22 UTC

External References:

https://bugs.exim.org/show_bug.cgi?id=2594

Comment 2 Michael Kaplan 2021-03-24 14:56:39 UTC

Created exim tracking bugs for this issue:

Affects: epel-all [bug 1942583]
Affects: fedora-all [bug 1942582]

Comment 3 Product Security DevOps Team 2021-03-24 17:35:18 UTC

This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.