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FreeBSD-SA-01:05 Security Advisory
Topic: stunnel contains potential remote compromise
Credits: Lez <lez@SCH.BME.HU>, Brian Hatch <bri@STUNNEL.ORG>
Affects: Ports collection prior to the correction date.
Vendor status: Updated version released
FreeBSD only: NO
stunnel is an SSL encryption wrapper for network services.
II. Problem Description
The stunnel port, versions prior to 3.9, contains a vulnerability
which could allow remote compromise. When debugging is turned on
(using the -d 7 option), stunnel will perform identd queries of remote
connections, and the username returned by the remote identd server is
written to the log file. Due to incorrect usage of syslog(), a
malicious remote user who can manipulate their identd username can
take advantage of string-formatting operators to execute arbitrary
code on the local system as the user running stunnel, often the root
The stunnel port is not installed by default, nor is it "part of
FreeBSD" as such: it is part of the FreeBSD ports collection, which
contains nearly 4500 third-party applications in a ready-to-install
format. The ports collections shipped with FreeBSD 3.5.1 and 4.2
contain this problem since it was discovered after the releases.
FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security
audit of the most security-critical ports.
Malicious remote users may execute arbitrary code on the local system
as the user running stunnel using stunnel, under certain circumstances.
If you have not chosen to install the stunnel port/package, then your
system is not vulnerable to this problem.
Deinstall the stunnel port/package, if you have installed it.
One of the following:
1) Upgrade your entire ports collection and rebuild the stunnel port.
2) Deinstall the old package and install a new package dated after the
correction date, obtained from:
3) download a new port skeleton for the stunnel port from:
and use it to rebuild the port.
4) Use the portcheckout utility to automate option (3) above. The
portcheckout port is available in /usr/ports/devel/portcheckout or the
package can be obtained from:
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