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Bypassing Cisco SNMP Access Lists Using Spoofed SNMP Requests
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SUMMARY
Under certain conditions, it is possible to bypass the SNMP ACL on Cisco
routers and gain ANMP Read / Write privileges.
DETAILS
In order to gain R/W SNMP access on the router, the following conditions
must exist:
a) RW community string is known
b) Access list policy is known
c) Access to the SNMP RW command will occur from the a.b.c.d network
(External).
d) No access lists present on TFTP server address.
Under these conditions, if the server holds an ACL like:
access-list 1 permit 192.168.1.0 0.0.0.255
snmp-server community public RO
snmp-server community datest RW 1
By spoofing an SNMP packet, it is possible to bypass the ACL. The idea is
to spoof a packet with a different source IP than the attacker has or more
accurately, a source IP which is allowed by the Router SNMP ACL.
Workarounds:
Enforce an ACL on the TFTP used in conjunction with the router, or disable
SMNP if possible.
ADDITIONAL INFORMATION
The information has been provided by <mailto:mati@see-security.com> muts.
The original article can be found at:
<http://new.remote-exploit.org/index.php/SNMP_Spoof>
http://new.remote-exploit.org/index.php/SNMP_Spoof
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