net-snmp bundles software for generating and retrieving SNMP data.
The netsnmp_udp_fmtaddr() function (snmplib/snmpUDPDomain.c), when using TCP wrappers for client authorization, does not properly parse hosts.allow rules.
A remote, unauthenticated attacker could bypass the ACL filtering, possibly resulting in the execution of arbitrary SNMP queries.
If possible, protect net-snmp with custom iptables rules:
iptables -s [client] -d [host] -p udp --dport 161 -j ACCEPT
iptables -s 0.0.0.0/0 -d [host] -p udp --dport 161 -j DROP
All net-snmp users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-analyzer/net-snmp-5.4.2.1-r1"