Bug 1942581 - exim: CNAME handling can break TLS certificate verification
Summary: exim: CNAME handling can break TLS certificate verification
Keywords:
Status: CLOSED UPSTREAM
Alias: None
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
Depends On: 1942582 1942583
Blocks:
TreeView+ depends on / blocked
 
Reported: 2021-03-24 14:56 UTC by Michael Kaplan
Modified: 2021-03-24 17:35 UTC (History)
3 users (show)

Fixed In Version:
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Last Closed: 2021-03-24 17:35:18 UTC
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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.
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