[UNIX] Remote Vulnerabilties in mod_ntlm

From: support@securiteam.com
Date: 04/21/03

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    From: support@securiteam.com
    To: list@securiteam.com
    Date: 21 Apr 2003 21:00:38 +0200
    
    

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      Remote Vulnerabilties in mod_ntlm
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.sourceforge.net/projects/modntlm> mod_ntlm is an Apache
    module (originally designed for Apache 1.3, now available for Apache 2.0)
    that provides the ability for Apache services to authenticate users via
    the NTLM authentication technology that is largely specific to Microsoft
    IIS.

    The module has been found to contain a pair of remotely exploitable
    vulnerabilities that would allow attacker to cause the server to execute
    arbitrary code.

    DETAILS

    Vulnerable systems:
     * Apache 1.3: mod_ntlm v0.4 and prior
     * Apache 2.0: mod_ntlmv2 v0.1

    mod_ntlm contains a pair of remotely exploitable vulnerabilities in its
    data logging routine. The vulnerabilities occur in a default build. The
    mod_ntlm "log()" function contains a pair of exploitable error conditions:

    static void
    log(const request_rec * r, const char *format,...)
    {
        va_list ap;
        char *s;

        if ((s = (char *) malloc(2048)) == NULL)
            return;
        va_start(ap, format);
        vsprintf(s, format, ap);
        va_end(ap);
        ap_log_rerror(APLOG_MARK, APLOG_NOERRNO | APLOG_NOTICE, r, s);
        free(s);
    }

    The function is called with user-supplied input in various locations in
    the code. The first vulnerability is a heap overflow -- if any
    user-supplied input is greater than 2048 characters, memory management
    structures are overwritten, and arbitrary code execution is possible.
    Secondly, an incorrect call to ap_log_rerror(). The last parameter to
    ap_log_rerror() is not a log line, but a format string. Due to the
    previous decoding operation, it becomes possible to pass format specifiers
    to ap_log_rerror(). A carefully crafted format string may allow code
    execution.

    Proof-of-Concept:
    Either of the following two sessions will cause httpd to exit due to
    segmentation fault:

    GET / HTTP/1.0
    Authorization: [Ax3000]

    Or

    GET / HTTP/1.0
    Authorization: %n%n%n%n

    Similarly, a proxy server can be exploited by using an external URL
    (http://www.yahoo.com/, for instance), in place of "/", and using
    Proxy-Authorization, in place of Authorization in the examples above.

    Vendor Status:
    The vulnerability was submitted to the vendor via SourceForge at:
    <http://sourceforge.net/tracker/index.php?func=detail&aid=723468&group_id=4906&atid=104906> http://sourceforge.net/tracker/index.php?func=detail&aid=723468&group_id=4906&atid=104906

    The vendor has not responded to the bug report as of the time of writing
    of this advisory.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:mattmurphy@kc.rr.com>
    Matthew Murphy.

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