haproxy crashes with a segmentation fault

Whenever I attempt to get a new certificate, my haproxy service crashes with a segmentation fault.

00000266:production_webserver_frontend.accept(0007)=0010 from [66.133.109.36:49292]
00000266:production_webserver_frontend.clireq[0010:ffffffff]: GET /.well-known/acme-challenge/token HTTP/1.1
00000266:production_webserver_frontend.clihdr[0010:ffffffff]: Host: site.example.com
00000266:production_webserver_frontend.clihdr[0010:ffffffff]: User-Agent: Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org)
00000266:production_webserver_frontend.clihdr[0010:ffffffff]: Accept: */*
00000266:production_webserver_frontend.clihdr[0010:ffffffff]: Accept-Encoding: gzip
00000266:production_webserver_frontend.clihdr[0010:ffffffff]: Connection: close
[info] 314/131321 (25402) : [acme] served http-01 token: token (client-ip: 66.133.109.36)
00000266:production_sites_nosni_be.srvrep[0010:ffffffff]: HTTP/1.1 200 OK
00000266:production_sites_nosni_be.srvhdr[0010:ffffffff]: Content-Type: text/plain
00000266:production_sites_nosni_be.srvhdr[0010:ffffffff]: Content-Length: 88
00000266:production_sites_nosni_be.srvhdr[0010:ffffffff]: Server: haproxy/acme-http01-authenticator
00000266:production_sites_nosni_be.srvhdr[0010:ffffffff]: Connection: close
Segmentation fault

No source file or test is named. Start with the supplied HAProxy log and reproduce the ACME HTTP-01 request through the plugin, then trace the segmentation fault; done means certificate validation no longer crashes HAProxy.

Written by the indexing model from the issue text.