Editing Simple Network Management Protocol (section)

=== Authentication ===
SNMP is available in different versions, and each version has its own security issues. SNMP v1 sends passwords in [[plaintext]] over the network. Therefore, passwords can be read with [[packet sniffing]]. SNMP v2 allows [[password hashing]] with [[MD5]], but this has to be configured. Virtually all [[network management software]] support SNMP v1, but not necessarily SNMP v2 or v3. SNMP v2 was specifically developed to provide [[data security]], that is [[authentication]], [[privacy]] and [[authorization]], but only SNMP version 2c gained the endorsement of the [[Internet Engineering Task Force]] (IETF), while versions 2u and 2* failed to gain IETF approval due to security issues. SNMP v3 uses MD5, [[Secure Hash Algorithm]] (SHA) and keyed algorithms to offer protection against unauthorized data modification and [[spoofing attack]]s. If a higher level of security is needed the [[Data Encryption Standard]] (DES) can be optionally used in the [[cipher block chaining]] mode. SNMP v3 is implemented on Cisco IOS since release 12.0(3)T.<ref name="Mason"/>{{rp|52}}

SNMPv3 may be subject to [[Brute force attack|brute force]] and [[dictionary attack]]s for guessing the authentication keys, or encryption keys, if these keys are generated from short (weak) passwords or passwords that can be found in a dictionary. SNMPv3 allows both providing random uniformly distributed cryptographic keys and generating cryptographic keys from a password supplied by the user. The risk of guessing authentication strings from hash values transmitted over the network depends on the [[cryptographic hash function]] used and the length of the hash value. SNMPv3 uses the [[HMAC]]-[[SHA-2]] [[authentication protocol]] for the User-based Security Model (USM).<ref name="RFC7630">{{cite IETF |RFC=7630 |title=HMAC-SHA-2 Authentication Protocols in the User-based Security Model (USM) for SNMPv3}}</ref> SNMP does not use a more secure [[challenge-handshake authentication protocol]]. SNMPv3 (like other SNMP protocol versions) is a [[stateless protocol]], and it has been designed with a minimal amount of interactions between the agent and the manager. Thus introducing a challenge-response handshake for each command would impose a burden on the agent (and possibly on the network itself) that the protocol designers deemed excessive and unacceptable.{{Citation needed|date=April 2017}}

The security deficiencies of all SNMP versions can be mitigated by [[IPsec]] authentication and confidentiality mechanisms.{{Citation needed|date=June 2020}} SNMP also may be carried securely over [[Datagram Transport Layer Security]] (DTLS).<ref name="Jacobs"/>

Many SNMP implementations include a type of automatic discovery where a new network component, such as a switch or router, is discovered and polled automatically. In SNMPv1 and SNMPv2c this is done through a ''community string'' that is transmitted in clear-text to other devices.<ref name="Jacobs"/> Clear-text passwords are a significant security risk. Once the community string is known outside the organization it could become the target for an attack. To alert administrators of other attempts to glean community strings, SNMP can be configured to pass community-name authentication failure traps.<ref name="Mason"/>{{rp|54}} If SNMPv2 is used, the issue can be avoided by enabling password encryption on the SNMP agents of network devices.

The common default configuration for community strings are "public" for read-only access and "private" for read-write.<ref name="Tipton"/>{{rp|1874}} Because of the well-known defaults, SNMP topped the list of the [[SANS Institute]]'s Common Default Configuration Issues and was number ten on the SANS Top 10 Most Critical Internet Security Threats for the year 2000.<ref>{{Cite web | url=http://www.sans.org/top20/2000/ | title=SANS Institute - CIS Critical Security Controls}}</ref> System and network administrators frequently do not change these configurations.<ref name="Tipton"/>{{rp|1874}}

Whether it runs over TCP or UDP, SNMPv1 and v2 are vulnerable to [[IP spoofing]] attacks. With spoofing, attackers may bypass device access lists in agents that are implemented to restrict SNMP access. SNMPv3 security mechanisms such as USM or TSM can prevent spoofing attacks.