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Description of problem:
There's a tiny race condition in stunnel that could lead to file descriptor leaks. The following blog post describes the problem in a general way:
http://udrepper.livejournal.com/20407.html

Upstream release notes for version 4.35 (initial fix) and 4.36 (additional, related fix).
http://stunnel.mirt.net/pipermail/stunnel-announce/2011-February/000051.html
http://stunnel.mirt.net/pipermail/stunnel-announce/2011-May/000052.html

Version-Release number of selected component (if applicable):
Likely all of them.

How reproducible:
Sorry, no reproducers.

This request was evaluated by Red Hat Product Management for
inclusion in the current release of Red Hat Enterprise Linux.
Because the affected component is not scheduled to be updated
in the current release, Red Hat is unable to address this
request at this time.

Red Hat invites you to ask your support representative to
propose this request, if appropriate, in the next release of
Red Hat Enterprise Linux.

Fixed upstrea, and will be dealt in rhel7 so closing for rhel6 as stunnel does not seem to be on scheduled component.