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https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=5375

           Summary: Buffer overflow when handling SNMP users preferences
           Product: Wireshark
           Version: unspecified
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: Minor
          Priority: Low
         Component: Wireshark
        AssignedTo: wireshark-bugs@xxxxxxxxxxxxx
        ReportedBy: d0c.s4vage@xxxxxxxxx


Build Information:
Version 1.4.1 (SVN Rev 34476 from /trunk-1.4)

Copyright 1998-2010 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled with GTK+ 2.16.6, (32-bit) with GLib 2.22.4, with WinPcap (version
unknown), with libz 1.2.3, without POSIX capabilities, without libpcre, with
SMI
0.4.8, with c-ares 1.7.1, with Lua 5.1, without Python, with GnuTLS 2.8.5, with
Gcrypt 1.4.5, with MIT Kerberos, with GeoIP, with PortAudio V19-devel (built
Oct
11 2010), with AirPcap.

Running on Windows XP Service Pack 3, build 2600, with WinPcap version 4.1.2
(packet.dll version 4.1.0.2001), based on libpcap version 1.0 branch 1_0_rel0b
(20091008), GnuTLS 2.8.5, Gcrypt 1.4.5, without AirPcap.

Built using Microsoft Visual C++ 9.0 build 30729

Wireshark is Open Source Software released under the GNU General Public
License.

Check the man page and http://www.wireshark.org for more information.
--
In epan/dissectors/packet-snmp.c in the snmp_usm_password_to_key_sha1 function,
a stack-based buffer can be overflowed.  The function is:

3057 /*
3058    SHA1 Password to Key Algorithm COPIED from RFC 3414 A.2.2
3059  */
3060 
3061 static void
3062 snmp_usm_password_to_key_sha1(const guint8 *password, guint passwordlen,
3063                   const guint8 *engineID, guint engineLength,
3064                   guint8 *key)
3065 {
3066     sha1_context     SH;
3067     guint8     *cp, password_buf[72];
3068     guint32      password_index = 0;
3069     guint32      count = 0, i;
3070 
3071     sha1_starts(&SH);   /* initialize SHA */
3072 
3073     /**********************************************/
3074     /* Use while loop until we've done 1 Megabyte */
3075     /**********************************************/
3076     while (count < 1048576) {
3077         cp = password_buf;
3078         for (i = 0; i < 64; i++) {
3079             /*************************************************/
3080             /* Take the next octet of the password, wrapping */
3081             /* to the beginning of the password as necessary.*/
3082             /*************************************************/
3083             *cp++ = password[password_index++ % passwordlen];
3084         }
3085         sha1_update (&SH, password_buf, 64);
3086         count += 64;
3087     }
3088     sha1_finish(&SH, key);
3089 
3090     /*****************************************************/
3091     /* Now localize the key with the engineID and pass   */
3092     /* through SHA to produce final key                  */
3093     /* May want to ensure that engineLength <= 32,       */
3094     /* otherwise need to use a buffer larger than 72     */
3095     /*****************************************************/
3096     memcpy(password_buf, key, 20);
3097     memcpy(password_buf+20, engineID, engineLength);
3098     memcpy(password_buf+20+engineLength, key, 20);
3099 
3100     sha1_starts(&SH);
3101     sha1_update(&SH, password_buf, 40+engineLength);
3102     sha1_finish(&SH, key);
3103     return;
3104  }

If a sufficiently large engineID is passed to this function, the password_buf
buffer will be overflowed (line 3097). Also, the same function with the same
problem is present in asn1/snmp/packet-snmp-template.c (used by asn2wrs)

I marked this as having a minor severity, since it's not remotely exploitable-

--Nephi

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