The Quagga BGP daemon (bgpd) prior to version 1.2.3 has a bug in its parsing of "Capabilities" in BGP OPEN messages, in the bgp_packet.c:bgp_capability_msg_parse function. The parser can enter an infinite loop on invalid capabilities if a Multi-Protocol capability does not have a recognized AFI/SAFI, causing a denial of service.
https://www.debian.org/security/2018/dsa-4115
https://usn.ubuntu.com/3573-1/
https://security.gentoo.org/glsa/201804-17
https://lists.debian.org/debian-lts-announce/2018/02/msg00021.html
https://gogs.quagga.net/Quagga/quagga/src/master/doc/security/Quagga-2018-1975.txt
https://cert-portal.siemens.com/productcert/pdf/ssa-451142.pdf