[NEWS] Multiple Vulnerabilities in Snort Preprocessors (RPC, stream4)

From: support@securiteam.com
Date: 04/18/03

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Date: 18 Apr 2003 12:29:11 +0200

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      Multiple Vulnerabilities in Snort Preprocessors (RPC, stream4)
    ------------------------------------------------------------------------

    SUMMARY

    There are two vulnerabilities in the Snort Intrusion Detection System,
    each in a separate preprocessor module. Both vulnerabilities allow remote
    attackers to execute arbitrary code with the privileges of the user
    running Snort typically root.

    DETAILS

    Vulnerable systems:
     * Snort IDS, versions 1.8 through 2.0 RC1

    The Snort intrusion detection system ships with a variety of preprocessor
    modules that allow the user to selectively include additional
    functionality. Researchers from two independent organizations have
    discovered vulnerabilities in two of these modules, the RPC preprocessor,
    and the "stream4" TCP fragment reassembly preprocessor.

    For additional information regarding Snort, please see
    <http://www.snort.org/> http://www.snort.org/.

    VU#139129 - Heap overflow in Snort "stream4" preprocessor (CAN-2003-0029)
    Researchers at CORE Security Technologies have discovered a remotely
    exploitable heap overflow in the Snort "stream4" preprocessor module. This
    module allows Snort to reassemble TCP packet fragments for further
    analysis.

    To exploit this vulnerability, an attacker must disrupt the state tracking
    mechanism of the preprocessor module by sending a series of packets with
    crafted sequence numbers. This causes the module to bypass a check for
    buffer overflow attempts and allows the attacker to insert arbitrary code
    into the heap.

    For additional information, please read the Core Security Technologies
    Advisory located at
    <http://www.coresecurity.com/common/showdoc.php?idx=313&idxseccion=10>
    http://www.coresecurity.com/common/showdoc.php?idx=313&idxseccion=10

    This vulnerability affects Snort versions 1.8.x, 1.9.x, and 2.0 prior to
    RC1. Snort has published an advisory regarding this vulnerability; it is
    available at <http://www.snort.org/advisories/snort-2003-04-16-1.txt.>
    http://www.snort.org/advisories/snort-2003-04-16-1.txt.

    VU#916785 - Buffer overflow in Snort RPC preprocessor (CAN-2003-0033)
    Researchers at Internet Security Systems (ISS) have discovered a remotely
    exploitable buffer overflow in the Snort RPC preprocessor module. Martin
    Roesch, primary developer for Snort, described the vulnerability as
    follows:

    When the RPC decoder normalizes fragmented RPC records, it incorrectly
    checks the lengths of what is being normalized against the current packet
    size, leading to an overflow condition. The RPC preprocessor is enabled by
    default.

    For additional information, please read the ISS X-Force advisory located
    at <http://www.iss.net/issEn/delivery/xforce/alertdetail.jsp?oid=21951>
    http://www.iss.net/issEn/delivery/xforce/alertdetail.jsp?oid=21951

    This vulnerability affects Snort versions 1.8.x through 1.9.1 and version
    2.0 Beta.

    Impact:
    Both VU#139129 and VU#916785 allow remote attackers to execute arbitrary
    code with the privileges of the user running Snort, typically root. In
    addition, it is not necessary for the attacker to know the IP address of
    the Snort device they wish to attack; merely sending malicious traffic
    where it can be observed by an affected Snort sensor is sufficient to
    exploit these vulnerabilities.

    Solution:
    Upgrade to Snort 2.0

    Both VU#139129 and VU#916785 are addressed in Snort version 2.0, which is
    available at <http://www.snort.org/dl/snort-2.0.0.tar.gz>
    http://www.snort.org/dl/snort-2.0.0.tar.gz

    Binary-only versions of Snort are available from
    <http://www.snort.org/dl/binaries> http://www.snort.org/dl/binaries

    For information from other vendors that ship affected versions of Snort,
    please see Appendix A of this document.

    Disable affected preprocessor modules
    Sites that are unable to immediately upgrade affected Snort sensors may
    prevent exploitation of this vulnerability by commenting out the affected
    preprocessor modules in the "snort.conf" configuration file.

    To prevent exploitation of VU#139129, comment out the following line:
    preprocessor stream4_reassemble

    To prevent exploitation of VU#916785, comment out the following line:
    preprocessor rpc_decode: 111 32771

    After commenting out the affected modules, send a SIGHUP signal to the
    affected Snort process to update the configuration. Note that disabling
    these modules may have adverse affects on a sensor's ability to correctly
    process RPC record fragments and TCP packet fragments. In particular,
    disabling the "stream4" preprocessor module will prevent the Snort sensor
    from detecting a variety of IDS evasion attacks.

    Block outbound packets from Snort IDS systems
    You may be able limit an attacker's capabilities if the system is
    compromised by blocking all outbound traffic from the Snort sensor. While
    this workaround will not prevent exploitation of the vulnerability, it may
    make it more difficult for the attacker to create a useful exploit.

    Appendix A. - Vendor Information
    This appendix contains information provided by vendors for this advisory.
    As vendors report new information to the CERT/CC, we will update this
    section and note the changes in our revision history. If a particular
    vendor is not listed below, we have not received their comments.

    Apple Computer, Inc.
    Snort is not shipped with Mac OS X or Mac OS X Server.

    Ingrian Networks
    Ingrian Networks products are not susceptible to VU#139129 and VU#916785
    since they do not use Snort.

    Ingrian customers who are using the IDS Extender Service Engine to mirror
    cleartext data to a Snort-based IDS should upgrade their IDS software.

    NetBSD
    NetBSD does not include snort in the base system.

    Snort is available from the 3rd party software system, pkgsrc. Users who
    have installed net/snort, net/snort-mysql or net/snort-pgsql should update
    to a fixed version. pkgsrc/security/audit-packages can be used to keep up
    to date with these types of issues.

    Red Hat Inc.
    Not vulnerable. Red Hat does not ship Snort in any of our supported
    products.

    SGI
    SGI does not ship snort as part of IRIX.

    Snort
    Snort 2.0 has undergone an external third party professional security
    audit funded by Sourcefire.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:cert@cert.org> CERT.

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