A Security Vulnerability Relating to Certificate Handling in sendmail(1M) Versions Prior to 8.14.4 May Allow Server Identification Forgery

Category
Security

Release Phase
Resolved

In this Document
  Description
  Likelihood of Occurrence
  Possible Symptoms
  Workaround or Resolution
  Patches
  Modification History
  References

Applies to:

OpenSolaris Operating System - Version: All Versions and later [Release: and later ]
Sun Software > Operating Systems > Solaris Operating System
Sun SPARC Sun OS
x86
SUNBUG 6913961

Description

A security vulnerability related to X.509 certificates affects sendmail(1M) as shipped with Solaris. This vulnerability may allow a remote user who controls a server which communicates with sendmail in some way (either as a client or another server), to present a crafted certificate which would appear to have come from any system on the Internet, and would be incorrectly accepted as valid by sendmail.

Exploitation of this issue is considered difficult and would typically require redirecting sendmail to an incorrect server by some means such as leveraging an exploit in DNS. The specific impact would depend on the way sendmail is configured to use the X.509 certificates.

For example, if sendmail is configured to require that mail being sent to a certain domain will only be delivered to that domain's mail server if it has a valid certificate for that domain, then it may be possible for a remote user to impersonate that server by presenting a forged certificate. The remote user would first have to cause sendmail to connect to a server which he or she controls instead of the correct one.

This issue is also discussed in the following documents:

CVE 2009-4565 at http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-4565

and http://www.sendmail.org/releases/8.14.4#RS

Likelihood of Occurrence

This issue can occur in the following releases:

SPARC Platform

Solaris 10 with patch 120302-01 or later
OpenSolaris based upon builds snv_13 through snv_131

x86 Platform

Solaris 10 with patch 120303-01 or later
OpenSolaris based upon builds snv_13 through snv_131

Notes:

1. This issue only affects systems on which sendmail has been configured to use TLS with X.509 certificates. To determine if sendmail is running on a host and whether TLS is enabled, the mconnect(1) command can be used to connect to sendmail (if running), after which, the EHLO command will output the supported extensions.

For example:

$ mconnect mailserver
connecting to host mailserver (0.0.0.0), port 25
connection open
220 mailserver.sun.com ESMTP Sendmail 8.14.3+Sun/8.14.3; Mon, 18 Jan 2010 14:29:31 -0800ST)
EHLO sun.com
250-mailserver.sun.com Hello localhost [127.0.0.1], pleased to meet you 
[...]
250-STARTTLS

If "STARTTLS" appears in the list of supported extensions, the sendmail server may be vulnerable.

The sendmail configuration would determine how the certificates are used, and therefore what may be achieved by a user presenting a forged certificate. See the sendmail documentation for more information, for example, the file /etc/mail/cf/README under the heading 'STARTTLS'.

If sendmail is not running on the system the mconnect(1) command will report the following:

$ /usr/bin/mconnect
connecting to host localhost (127.0.0.1), port 25
connect: Connection refused

2. Sendmail shipped with Solaris 8 and 9 does not support TLS and those releases are not impacted.

Possible Symptoms

There are no predictable symptoms that would indicate that a forged certificate has been used with sendmail.

Workaround or Resolution

This issue is resolved in the following releases:

SPARC Platform

Solaris 10 with patch 142436-04 or later
OpenSolaris based upon builds snv_132 or later

x86 Platform

Solaris 10 with patch 142437-04 or later
OpenSolaris based upon builds snv_132 or later

Patches

142436-04
142437-04

Modification History

07-Jun-2010 - Updated for patch release, issue is Resolved

References

<PATCH:142437-04> -
sunpatch 142436-04

Attachments

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