IBM Information for VU#466239

IBM AIX line printer daemon contains a buffer overflow in chk_fhost()



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11 SEP 2001 0:53 GMT MSS-OAR-E01-2001:391.1
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Fri Sep 7 11:18:24 CDT 2001

VULNERABILITY: Buffer Overflow Vulnerabilities in lpd

PLATFORMS: IBM AIX 4.3 and 5.1

SOLUTION: Apply the emergency-fixes described below.

THREAT: Malicious user could obtain root privileges, or cause
a denial of service (DoS).

CERT Advisory: See CERT CA-2001-15 for info on
Solaris vulnerability. Also see the posting,, at the
Internet Security Systems site for info on BSD
implementations of lpd.

CVE Candidate: CAN-2001-0670

I. Description

The Line Printer daemon, lpd, shipped with AIX contains several
buffer overflow vulnerabilities that potentially allow a malicious
remote user to gain root privileges.

Two of the three vulnerabilities found require the attacker's system
be listed in /etc/hosts.lpd or /etc/hosts.equiv. The third requires
that the malicious user have control over the victim's domain name
server (DNS).

II. Impact

A malicious local or remote user can use a well-crafted exploit code
to gain root privileges on the attacked system, compromising the
integrity of the system and its attached local network.

If the malicious user is unable to gain root access, he or she could
still cause a system crash (DoS) via this vulnerability.

III. Solutions

A. Official fix

IBM is working on the following fixes which will be available soon:

AIX 4.3: APAR #IY23037
AIX 5.1: APAR #IY23041

NOTE: Fix will not be provided for versions prior to 4.3 as these
are no longer supported by IBM. Affected customers are urged to
upgrade to 4.3.3 at the latest maintenance level, or to 5.1, when it
becomes available.

B. How to minimize the vulnerability


None recommended.

IBM advises customers to disable the line printer daemon until an
efix or official APAR is installed.

In general, customers are advised to disable all unused daemon
services as good security practice.


Temporary fixes for AIX 4.3.x and 5.1 systems are available.

The temporary fixes can be downloaded via ftp from:

The efix tarball consists of two patched lpd binaries, one for AIX
4.3.x systems (lpd.43) and one for AIX 5.1 (scheduled for release
soon; binary is lpd.51). A copy of this Advisory is also included.

These temporary fixes have not been fully regression tested; thus,
IBM does not warrant the fully correct functioning of the efix.
Customers install the efix and operate the modified version of AIX at
their own risk.

To proceed with efix installation:

First, verify the MD5 cryptographic hash sums of each efix files you
obtain from unpacking the efix tarball with those given below. These
should match exactly; if they do not, double check the hash results
and the download site address. If OK, contact IBM AIX Security at and describe the discrepancy.

Filename sum md5
lpd.43X.tar 11225 20 3c7e6f0ef29b6147835213253de8f1bf
lpd.51B.tar 35507 80 38bc7f7516d76b8a89914fdab97e1377

Efix Installation Instructions:

1. Become root, if not already done.

2. In a scratch or tmp directory, uncompress and untar the efix:

a. uncompress lpd_efix.tar.Z
b. tar -xvf lpd_efix.tar

3. If you are running an AIX 4.3.x system, copy the lpd.43 file to
/usr/sbin. Do the same if you have AIX 5.1 running, except copy the
lpd.51 file.

4. Stop the lpd daemon if it is currently running:

a. stopsrc -s lpd

5. Make a backup copy of the existing lpd binary package in case
something goes wrong with the installation of the efix:

a. cp /usr/sbin/lpd /usr/sbin/lpd.original

6. Now copy the efix binary to take the place of the original lpd:

a. cp /usr/sbin/lpd.43 (or lpd.51, as appropriate)

7. Check to be certain that the new lpd is executable by root and is
assigned proper permissions otherwise.

8. Restart the lpd daemon:

a. startsrc -s lpd

IV. Obtaining Fixes

IBM AIX APARs may be ordered using Electronic Fix Distribution (via
the FixDist program), or from the IBM Support Center. For more
information on FixDist, and to obtain fixes via the Internet, please

or send email to "" with the word "FixDist" in
the "Subject:" line.

To facilitate ease of ordering all security related APARs for each
AIX release, security fixes are periodically bundled into a
cumulative APAR. For more information on these cumulative APARs
including last update and list of individual fixes, send email to
"" with the word "subscribe Security_APARs" in
the "Subject:" line.

V. Acknowledgements

Many thanks to Internet Security Services (ISS) for identifying these
vulnerabilities in lpd, and to the CERT/CC for preparing and
distributing the Vulnerability Notes provided to us vendors.

VI. Contact Information

Comments regarding the content of this announcement can be directed

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security vulnerabilities, send email to
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subscriptions, use a subject of "help".

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respective holders.

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Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Vendor References



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