Date: 17 October 2000
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AUSCERT External Security Bulletin Redistribution
ESB-2000.289 -- FreeBSD-SA-00:57
muh IRC bouncer remote vulnerability
17 October 2000
AusCERT Security Bulletin Summary
Vendor: FreeBSD Ports Collection
Operating System: FreeBSD
Impact: Execute Arbitrary Code/Commands
Access Required: Remote
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FreeBSD-SA-00:57 Security Advisory
Topic: muh IRC bouncer remote vulnerability
Credits: Maxime Henrion <mux@QUALYS.COM>
Affects: Ports collection prior to the correction date.
Corrected: 2000-09-10 (4.1.1-RELEASE)
Vendor status: Updated version released
FreeBSD only: NO
muh is an IRC bouncer, a program that allows a host to act as a relay
between an IRC client on a local/remote machine and the IRC server.
II. Problem Description
The muh port, versions 2.05c and before, contains a vulnerability
which allows remote users to gain the privileges of the user running
muh. This is accomplished by sending a carefully crafted exploit
string containing string format operators to a user using muh but who
is not connected. When the user reconnects and executes '/muh read',
muh will allow the remote attacker to execute arbitrary code as the
The muh 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 4000 third-party applications in a ready-to-install format.
The ports collections shipped with FreeBSD 3.5.1 and 4.1 contain this
problem since it was discovered after the releases, but it was
corrected prior to the release of FreeBSD 4.1.1.
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.
Remote IRC users can cause arbitrary code to be executed as the user
If you have not chosen to install the muh port/package, then your
system is not vulnerable to this problem.
Deinstall the muh port/package, if you you have installed it.
One of the following:
1) Upgrade your entire ports collection and rebuild the muh port.
2) Deinstall the old package and install a new package dated after the
correction date, obtained from:
NOTE: It may be several days before updated packages are available.
3) download a new port skeleton for the cvsweb 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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