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**SNMP - Simple Network Management Protocol** is a protocol used to monitor different devices in the network (like routers, switches, printers, IoTs...).
SNMP also uses the port **162/UDP** for **traps**. These are data **packets sent from the SNMP server to the client without being explicitly requested**.
To ensure that SNMP access works across manufacturers and with different client-server combinations, the **Management Information Base (MIB)** was created. MIB is an **independent format for storing device information**. A MIB is a **text** file in which all queryable **SNMP objects** of a device are listed in a **standardized** tree hierarchy. It contains at **least one `Object Identifier` (`OID`)**, which, in addition to the necessary **unique address** and a **name**, also provides information about the type, access rights, and a description of the respective object\
MIB files are written in the `Abstract Syntax Notation One` (`ASN.1`) based ASCII text format. The **MIBs do not contain data**, but they explain **where to find which information** and what it looks like, which returns values for the specific OID, or which data type is used.
**OIDs** stands for **O**bject **Id**entifiers. **OIDs uniquely identify managed objects in a MIB hierarchy**. This can be depicted as a tree, the levels of which are assigned by different organizations. Top level MIB object IDs (OIDs) belong to different standard organizations.\
You can **navigate** through an **OID tree** from the web here: [http://www.oid-info.com/cgi-bin/display?tree=#focus](http://www.oid-info.com/cgi-bin/display?tree=#focus) or **see what a OID means** (like `1.3.6.1.2.1.1`) accessing [http://oid-info.com/get/1.3.6.1.2.1.1](http://oid-info.com/get/1.3.6.1.2.1.1).\
There are some **well-known OIDs** like the ones inside [1.3.6.1.2.1](http://oid-info.com/get/1.3.6.1.2.1) that references MIB-2 defined Simple Network Management Protocol (SNMP) variables. And from the **OIDs pending from this one** you can obtain some interesting host data (system data, network data, processes data...)
* 1 – this is called the ISO and it establishes that this is an OID. This is why all OIDs start with “1”
* 3 – this is called ORG and it is used to specify the organization that built the device.
* 6 – this is the dod or the Department of Defense which is the organization that established the Internet first.
* 1 – this is the value of the internet to denote that all communications will happen through the Internet.
* 4 – this value determines that this device is made by a private organization and not a government one.
* 1 – this value denotes that the device is made by an enterprise or a business entity.
These first six values tend to be the same for all devices and they give you the basic information about them. This sequence of numbers will be the same for all OIDs, except when the device is made by the government.
* **SNMPv1**: Main one, it is still the most frequent, the **authentication is based on a string** (community string) that travels in **plain-text** (all the information travels in plain text). **Version 2 and 2c** send the **traffic in plain text** also and uses a **community string as authentication**.
* **SNMPv3**: Uses a better **authentication** form and the information travels **encrypted** using (**dictionary attack** could be performed but would be much harder to find the correct creds than in SNMPv1 and v2).
As mentioned before, **in order to access the information saved on the MIB you need to know the community string on versions 1 and 2/2c and the credentials on version 3.**\
Note that **the writability of an OID depends on the community string used**, so **even** if you find that "**public**" is being used, you could be able to **write some values.** Also, there **may** exist objects which are **always "Read Only".**\
In versions 1 and 2/2c if you to use a **bad** community string the server wont **respond**. So, if it responds, a **valid community strings was used**.
* The manager receives notifications ([Traps](https://en.wikipedia.org/wiki/Simple\_Network\_Management\_Protocol#Trap) and [InformRequests](https://en.wikipedia.org/wiki/Simple\_Network\_Management\_Protocol#InformRequest)) on port **162**.
* When used with [Transport Layer Security](https://en.wikipedia.org/wiki/Transport\_Layer\_Security) or [Datagram Transport Layer Security](https://en.wikipedia.org/wiki/Datagram\_Transport\_Layer\_Security), requests are received on port **10161** and notifications are sent to port **10162**.
To **guess the community string** you could perform a dictionary attack. Check [here different ways to perform a brute-force attack against SNMP](../../generic-methodologies-and-resources/brute-force.md#snmp). A frequently used community string is `public`.
**SNMP** has a lot of information about the host and things that you may find interesting are: **Network interfaces** (IPv4 and **IPv6** address), Usernames, Uptime, Server/OS version, and **processes**
[Braa ](https://github.com/mteg/braa)is a mass SNMP scanner. The intended usage of such a tool is, of course, making SNMP queries – but unlike snmpwalk from net-snmp, it is able to query dozens or hundreds of hosts simultaneously, and in a single process. Thus, it consumes very few system resources and does the scanning VERY fast.
Braa implements its OWN snmp stack, so it does NOT need any SNMP libraries like net-snmp.
So, lets look for the most interesting information (from [https://blog.rapid7.com/2016/05/05/snmp-data-harvesting-during-penetration-testing/](https://blog.rapid7.com/2016/05/05/snmp-data-harvesting-during-penetration-testing/)):
One of the first things I do is extract the sysDesc .1.3.6.1.2.1.1.1.0 MIB data from each file to determine what devices I have harvested information from. This can easily be done using the following grep command:
As an example, if I can identify the private community string used by an organization on their Cisco IOS routers, then I could possibly use that community string to extract the running configurations from those routers. The best method for finding such data has often been related to SNMP Trap data. So again, using the following grep we can parse through a lot of MIB data quickly searching for the key word of “trap”:
Another area of interest is logs, I have discovered that there are some devices that hold logs within the MIB tables. These logs can also contain failed logon attempts. Think about the last time you logged into a device via Telnet or SSH and inadvertently entered your password as the username. I typically search for key words such as _fail_, _failed_ or _login_ and examine that data to see if there is anything of value.
If there is an ACL that only allows some IPs to query the SMNP service, you can spoof one of this addresses inside the UDP packet an sniff the traffic.
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