SNMP Attack

• Ports used

  • [[UDP]] 161

  • [[UDP]] 162

    • traps

    • These are data packets sent from the SNMP server to the client without being explicitly requested.

      • If a device is configured accordingly

    • An SNMP trap is sent to the client once a specific event occurs on the server-side

MIB

• To ensure that SNMP access works across manufacturers and with different client-server combinations, the Management Information Base (MIB) was created.

  • A MIB is a text file in which all queryable SNMP objects of a device are listed in a standardized tree hierarchy

• do not contain data

  • link to the data

    • returns a specific OID

OID

• represents a node in a hierarchical namespace.

• A sequence of numbers uniquely identifies each node, allowing the node's position in the tree to be determined.

SNMP

SNMPv1

• provides traps,

• no built-in authentication mechanism

• does not support encryption

SNMPv2

• similar to SNMPv1

• community string that provides security is only transmitted in plain text, meaning it has no built-in encryption.

SNMPv3

• has authentication using username and password and transmission encryption (via pre-shared key) of the data

Default Configuration

cat /etc/snmp/snmpd.conf | grep -v "#" | sed -r '/^\s*$/d'

sysLocation    Sitting on the Dock of the Bay
sysContact     Me <[e-mail]>
sysServices    72
master  agentx
agentaddress  127.0.0.1,[::1]
view   systemonly  included   .1.3.6.1.2.1.1
view   systemonly  included   .1.3.6.1.2.1.25.1
rocommunity  public default -V systemonly
rocommunity6 public default -V systemonly
rouser authPrivUser authpriv -V systemonly

Dangerous Settings

Settings	Description
rwuser noauth	Provides access to the full OID tree without authentication.
rwcommunity <community string> <IPv4 address>	Provides access to the full OID tree regardless of where the requests were sent from.
rwcommunity6 <community string> <IPv6 address>	Same access as with rwcommunity with the difference of using IPv6.

---

Footprinting the Service

snmpwalk

• snmpwalk

snmpwalk -v 2c -c public monitored.htb -m all| tee snmp_data

snmpwalk -v2c -c public 10.129.14.128

iso.3.6.1.2.1.1.1.0 = STRING: "Linux htb 5.11.0-34-generic #36~20.04.1-Ubuntu SMP Fri Aug 27 08:06:32 UTC 2021 x86_64"
iso.3.6.1.2.1.1.2.0 = OID: iso.3.6.1.4.1.8072.3.2.10
iso.3.6.1.2.1.1.3.0 = Timeticks: (5134) 0:00:51.34
iso.3.6.1.2.1.1.4.0 = STRING: "[e-mail]"
iso.3.6.1.2.1.1.5.0 = STRING: "htb"
iso.3.6.1.2.1.1.6.0 = STRING: "Sitting on the Dock of the Bay"
iso.3.6.1.2.1.1.7.0 = INTEGER: 72
iso.3.6.1.2.1.1.8.0 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.2.1 = OID: iso.3.6.1.6.3.10.3.1.1
iso.3.6.1.2.1.1.9.1.2.2 = OID: iso.3.6.1.6.3.11.3.1.1
iso.3.6.1.2.1.1.9.1.2.3 = OID: iso.3.6.1.6.3.15.2.1.1
iso.3.6.1.2.1.1.9.1.2.4 = OID: iso.3.6.1.6.3.1
iso.3.6.1.2.1.1.9.1.2.5 = OID: iso.3.6.1.6.3.16.2.2.1
iso.3.6.1.2.1.1.9.1.2.6 = OID: iso.3.6.1.2.1.49
iso.3.6.1.2.1.1.9.1.2.7 = OID: iso.3.6.1.2.1.4
iso.3.6.1.2.1.1.9.1.2.8 = OID: iso.3.6.1.2.1.50
iso.3.6.1.2.1.1.9.1.2.9 = OID: iso.3.6.1.6.3.13.3.1.3
iso.3.6.1.2.1.1.9.1.2.10 = OID: iso.3.6.1.2.1.92
iso.3.6.1.2.1.1.9.1.3.1 = STRING: "The SNMP Management Architecture MIB."
iso.3.6.1.2.1.1.9.1.3.2 = STRING: "The MIB for Message Processing and Dispatching."
iso.3.6.1.2.1.1.9.1.3.3 = STRING: "The management information definitions for the SNMP User-based Security Model."
iso.3.6.1.2.1.1.9.1.3.4 = STRING: "The MIB module for SNMPv2 entities"
iso.3.6.1.2.1.1.9.1.3.5 = STRING: "View-based Access Control Model for SNMP."
iso.3.6.1.2.1.1.9.1.3.6 = STRING: "The MIB module for managing TCP implementations"
iso.3.6.1.2.1.1.9.1.3.7 = STRING: "The MIB module for managing IP and ICMP implementations"
iso.3.6.1.2.1.1.9.1.3.8 = STRING: "The MIB module for managing UDP implementations"
iso.3.6.1.2.1.1.9.1.3.9 = STRING: "The MIB modules for managing SNMP Notification, plus filtering."
iso.3.6.1.2.1.1.9.1.3.10 = STRING: "The MIB module for logging SNMP Notifications."
iso.3.6.1.2.1.1.9.1.4.1 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.2 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.3 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.4 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.5 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.6 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.7 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.8 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.9 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.1.9.1.4.10 = Timeticks: (0) 0:00:00.00
iso.3.6.1.2.1.25.1.1.0 = Timeticks: (3676678) 10:12:46.78
iso.3.6.1.2.1.25.1.2.0 = Hex-STRING: 07 E5 09 14 0E 2B 2D 00 2B 02 00 
iso.3.6.1.2.1.25.1.3.0 = INTEGER: 393216
iso.3.6.1.2.1.25.1.4.0 = STRING: "BOOT_IMAGE=/boot/vmlinuz-5.11.0-34-generic root=UUID=9a6a5c52-f92a-42ea-8ddf-940d7e0f4223 ro quiet splash"
iso.3.6.1.2.1.25.1.5.0 = Gauge32: 3
iso.3.6.1.2.1.25.1.6.0 = Gauge32: 411
iso.3.6.1.2.1.25.1.7.0 = INTEGER: 0
iso.3.6.1.2.1.25.1.7.0 = No more variables left in this MIB View (It is past the end of the MIB tree)

...SNIP...

iso.3.6.1.2.1.25.6.3.1.2.1232 = STRING: "printer-driver-sag-gdi_0.1-7_all"
iso.3.6.1.2.1.25.6.3.1.2.1233 = STRING: "printer-driver-splix_2.0.0+svn315-7fakesync1build1_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1234 = STRING: "procps_2:3.3.16-1ubuntu2.3_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1235 = STRING: "proftpd-basic_1.3.6c-2_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1236 = STRING: "proftpd-doc_1.3.6c-2_all"
iso.3.6.1.2.1.25.6.3.1.2.1237 = STRING: "psmisc_23.3-1_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1238 = STRING: "publicsuffix_20200303.0012-1_all"
iso.3.6.1.2.1.25.6.3.1.2.1239 = STRING: "pulseaudio_1:13.99.1-1ubuntu3.12_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1240 = STRING: "pulseaudio-module-bluetooth_1:13.99.1-1ubuntu3.12_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1241 = STRING: "pulseaudio-utils_1:13.99.1-1ubuntu3.12_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1242 = STRING: "python-apt-common_2.0.0ubuntu0.20.04.6_all"
iso.3.6.1.2.1.25.6.3.1.2.1243 = STRING: "python3_3.8.2-0ubuntu2_amd64"
iso.3.6.1.2.1.25.6.3.1.2.1244 = STRING: "python3-acme_1.1.0-1_all"
iso.3.6.1.2.1.25.6.3.1.2.1245 = STRING: "python3-apport_2.20.11-0ubuntu27.21_all"
iso.3.6.1.2.1.25.6.3.1.2.1246 = STRING: "python3-apt_2.0.0ubuntu0.20.04.6_amd64" 

snmpbulkwalk

• faster than snmp walk

snmpbulkwalk -v 2c -c public monitored.htb -m all| tee snmp_data

OneSixtyOne

• can be used to get community string

• https://github.com/trailofbits/onesixtyone

sudo apt install onesixtyone

onesixtyone -c /opt/useful/SecLists/Discovery/SNMP/snmp.txt 10.129.14.128

Scanning 1 hosts, 3220 communities
10.129.14.128 [public] Linux htb 5.11.0-37-generic #41~20.04.2-Ubuntu SMP Fri Sep 24 09:06:38 UTC 2021 x86_64

• Once we know a community string, we can use it with braa to brute-force the individual OIDs and enumerate the information behind them.

Braa

 sudo apt install braa

 braa <community string>@<IP>:.1.3.6.* 

braa public@10.129.14.128:.1.3.6.*