CVE-2024-33655 (published 2024-06-06T17:15Z)

The DNS protocol in RFC 1035 and updates allows remote attackers to cause a denial of service (resource consumption) by arranging for DNS queries to be accumulated for seconds, such that responses are later sent in a pulsing burst (which can be considered traffic amplification in some cases), aka the "DNSBomb" issue.


Weakness information:
cwe_id: NVD-CWE-noinfo
cwe_name: Insufficient Information
description: There is insufficient information about the issue to classify it; details are unkown or unspecified.
extended_description: Insufficient Information

Fix information:
repo_url: https://github.com/NLnetLabs/unbound
commit_details: repo_url: https://github.com/NLnetLabs/unbound
author: W.C.A. Wijngaards
author_date: 2024-05-01 10:10:58+02:00
msg: - Fix for the DNSBomb vulnerability CVE-2024-33655. Thanks to Xiang Li
  from the Network and Information Security Lab of Tsinghua University
  for reporting it.
repository: repo_url: https://github.com/NLnetLabs/unbound
repo_name: NLnetLabs/unbound
description: Unbound is a validating, recursive, and caching DNS resolver.
repo_language: C
owner: NLnetLabs
file_changes: filename: Changelog
change_type: ModificationType.MODIFY
diff: @@ -1,3 +1,8 @@
+1 May 2024: Wouter
+	- Fix for the DNSBomb vulnerability CVE-2024-33655. Thanks to Xiang Li
+	  from the Network and Information Security Lab of Tsinghua University
+	  for reporting it.
+
 29 April 2024: Yorgos
 	- Cleanup unnecessary strdup calls for EDE strings.
 

programming_language: Markdown
filename: example.conf.in
change_type: ModificationType.MODIFY
diff: @@ -191,6 +191,21 @@ server:
 	# are behind a slow satellite link, to eg. 1128.
 	# unknown-server-time-limit: 376
 
+	# msec before recursion replies are dropped. The work item continues.
+	# discard-timeout: 1900
+
+	# Max number of replies waiting for recursion per IP address.
+	# wait-limit: 1000
+
+	# Max replies waiting for recursion for IP address with cookie.
+	# wait-limit-cookie: 10000
+
+	# Apart from the default, the wait limit can be set for a netblock.
+	# wait-limit-netblock: 192.0.2.0/24 50000
+
+	# Apart from the default, the wait limit with cookie can be adjusted.
+	# wait-limit-cookie-netblock: 192.0.2.0/24 50000
+
 	# the amount of memory to use for the RRset cache.
 	# plain value in bytes or you can append k, m or G. default is "4Mb".
 	# rrset-cache-size: 4m

programming_language: Markdown
filename: unbound.conf.5.in
change_type: ModificationType.MODIFY
diff: @@ -302,6 +302,36 @@ Increase this if you are behind a slow satellite link, to eg. 1128.
 That would then avoid re\-querying every initial query because it times out.
 Default is 376 msec.
 .TP
+.B discard\-timeout: \fI<msec>
+The wait time in msec where recursion requests are dropped. This is
+to stop a large number of replies from accumulating. They receive
+no reply, the work item continues to recurse. It is nice to be a bit
+larger than serve\-expired\-client\-timeout if that is enabled.
+A value of 1900 msec is suggested. The value 0 disables it.
+Default 1900 msec.
+.TP
+.B wait\-limit: \fI<number>
+The number of replies that can wait for recursion, for an IP address.
+This makes a ratelimit per IP address of waiting replies for recursion.
+It stops very large amounts of queries waiting to be returned to one
+destination. The value 0 disables wait limits. Default is 1000.
+.TP
+.B wait\-limit\-cookie: \fI<number>
+The number of replies that can wait for recursion, for an IP address
+that sent the query with a valid DNS cookie. Since the cookie validates
+the client address, the limit can be higher. Default is 10000.
+.TP
+.B wait\-limit\-netblock: \fI<netblock> <number>
+The wait limit for the netblock. If not given the wait\-limit value is
+used. The most specific netblock is used to determine the limit. Useful for
+overriding the default for a specific, group or individual, server.
+The value -1 disables wait limits for the netblock.
+.TP
+.B wait\-limit\-cookie\-netblock: \fI<netblock> <number>
+The wait limit for the netblock, when the query has a DNS cookie.
+If not given, the wait\-limit\-cookie value is used.
+The value -1 disables wait limits for the netblock.
+.TP
 .B so\-rcvbuf: \fI<number>
 If not 0, then set the SO_RCVBUF socket option to get more buffer
 space on UDP port 53 incoming queries.  So that short spikes on busy

programming_language: Go
filename: infra.c
change_type: ModificationType.MODIFY
diff: @@ -234,6 +234,81 @@ setup_domain_limits(struct infra_cache* infra, struct config_file* cfg)
 	return 1;
 }
 
+/** find or create element in wait limit netblock tree */
+static struct wait_limit_netblock_info*
+wait_limit_netblock_findcreate(struct infra_cache* infra, char* str,
+	int cookie)
+{
+	rbtree_type* tree;
+	struct sockaddr_storage addr;
+	int net;
+	socklen_t addrlen;
+	struct wait_limit_netblock_info* d;
+
+	if(!netblockstrtoaddr(str, 0, &addr, &addrlen, &net)) {
+		log_err("cannot parse wait limit netblock '%s'", str);
+		return 0;
+	}
+
+	/* can we find it? */
+	if(cookie)
+		tree = &infra->wait_limits_cookie_netblock;
+	else
+		tree = &infra->wait_limits_netblock;
+	d = (struct wait_limit_netblock_info*)addr_tree_find(tree, &addr,
+		addrlen, net);
+	if(d)
+		return d;
+
+	/* create it */
+	d = (struct wait_limit_netblock_info*)calloc(1, sizeof(*d));
+	if(!d)
+		return NULL;
+	d->limit = -1;
+	if(!addr_tree_insert(tree, &d->node, &addr, addrlen, net)) {
+		log_err("duplicate element in domainlimit tree");
+		free(d);
+		return NULL;
+	}
+	return d;
+}
+
+
+/** insert wait limit information into lookup tree */
+static int
+infra_wait_limit_netblock_insert(struct infra_cache* infra,
+	struct config_file* cfg)
+{
+	struct config_str2list* p;
+	struct wait_limit_netblock_info* d;
+	for(p = cfg->wait_limit_netblock; p; p = p->next) {
+		d = wait_limit_netblock_findcreate(infra, p->str, 0);
+		if(!d)
+			return 0;
+		d->limit = atoi(p->str2);
+	}
+	for(p = cfg->wait_limit_cookie_netblock; p; p = p->next) {
+		d = wait_limit_netblock_findcreate(infra, p->str, 1);
+		if(!d)
+			return 0;
+		d->limit = atoi(p->str2);
+	}
+	return 1;
+}
+
+/** setup wait limits tree (0 on failure) */
+static int
+setup_wait_limits(struct infra_cache* infra, struct config_file* cfg)
+{
+	addr_tree_init(&infra->wait_limits_netblock);
+	addr_tree_init(&infra->wait_limits_cookie_netblock);
+	if(!infra_wait_limit_netblock_insert(infra, cfg))
+		return 0;
+	addr_tree_init_parents(&infra->wait_limits_netblock);
+	addr_tree_init_parents(&infra->wait_limits_cookie_netblock);
+	return 1;
+}
+
 struct infra_cache* 
 infra_create(struct config_file* cfg)
 {
@@ -267,6 +342,10 @@ infra_create(struct config_file* cfg)
 		infra_delete(infra);
 		return NULL;
 	}
+	if(!setup_wait_limits(infra, cfg)) {
+		infra_delete(infra);
+		return NULL;
+	}
 	infra_ip_ratelimit = cfg->ip_ratelimit;
 	infra->client_ip_rates = slabhash_create(cfg->ip_ratelimit_slabs,
 	    INFRA_HOST_STARTSIZE, cfg->ip_ratelimit_size, &ip_rate_sizefunc,
@@ -287,6 +366,12 @@ static void domain_limit_free(rbnode_type* n, void* ATTR_UNUSED(arg))
 	}
 }
 
+/** delete wait_limit_netblock_info entries */
+static void wait_limit_netblock_del(rbnode_type* n, void* ATTR_UNUSED(arg))
+{
+	free(n);
+}
+
 void 
 infra_delete(struct infra_cache* infra)
 {
@@ -296,6 +381,10 @@ infra_delete(struct infra_cache* infra)
 	slabhash_delete(infra->domain_rates);
 	traverse_postorder(&infra->domain_limits, domain_limit_free, NULL);
 	slabhash_delete(infra->client_ip_rates);
+	traverse_postorder(&infra->wait_limits_netblock,
+		wait_limit_netblock_del, NULL);
+	traverse_postorder(&infra->wait_limits_cookie_netblock,
+		wait_limit_netblock_del, NULL);
 	free(infra);
 }
 
@@ -880,7 +969,8 @@ static void infra_create_ratedata(struct infra_cache* infra,
 
 /** create rate data item for ip address */
 static void infra_ip_create_ratedata(struct infra_cache* infra,
-	struct sockaddr_storage* addr, socklen_t addrlen, time_t timenow)
+	struct sockaddr_storage* addr, socklen_t addrlen, time_t timenow,
+	int mesh_wait)
 {
 	hashvalue_type h = hash_addr(addr, addrlen, 0);
 	struct ip_rate_key* k = (struct ip_rate_key*)calloc(1, sizeof(*k));
@@ -898,6 +988,7 @@ static void infra_ip_create_ratedata(struct infra_cache* infra,
 	k->entry.data = d;
 	d->qps[0] = 1;
 	d->timestamp[0] = timenow;
+	d->mesh_wait = mesh_wait;
 	slabhash_insert(infra->client_ip_rates, h, &k->entry, d, NULL);
 }
 
@@ -1121,6 +1212,81 @@ int infra_ip_ratelimit_inc(struct infra_cache* infra,
 	}
 
 	/* create */
-	infra_ip_create_ratedata(infra, addr, addrlen, timenow);
+	infra_ip_create_ratedata(infra, addr, addrlen, timenow, 0);
 	return 1;
 }
+
+int infra_wait_limit_allowed(struct infra_cache* infra, struct comm_reply* rep,
+	int cookie_valid, struct config_file* cfg)
+{
+	struct lruhash_entry* entry;
+	if(cfg->wait_limit == 0)
+		return 1;
+
+	entry = infra_find_ip_ratedata(infra, &rep->client_addr,
+		rep->client_addrlen, 0);
+	if(entry) {
+		rbtree_type* tree;
+		struct wait_limit_netblock_info* w;
+		struct rate_data* d = (struct rate_data*)entry->data;
+		int mesh_wait = d->mesh_wait;
+		lock_rw_unlock(&entry->lock);
+
+		/* have the wait amount, check how much is allowed */
+		if(cookie_valid)
+			tree = &infra->wait_limits_cookie_netblock;
+		else	tree = &infra->wait_limits_netblock;
+		w = (struct wait_limit_netblock_info*)addr_tree_lookup(tree,
+			&rep->client_addr, rep->client_addrlen);
+		if(w) {
+			if(w->limit != -1 && mesh_wait > w->limit)
+				return 0;
+		} else {
+			/* if there is no IP netblock specific information,
+			 * use the configured value. */
+			if(mesh_wait > (cookie_valid?cfg->wait_limit_cookie:
+				cfg->wait_limit))
+				return 0;
+		}
+	}
+	return 1;
+}
+
+void infra_wait_limit_inc(struct infra_cache* infra, struct comm_reply* rep,
+	time_t timenow, struct config_file* cfg)
+{
+	struct lruhash_entry* entry;
+	if(cfg->wait_limit == 0)
+		return;
+
+	/* Find it */
+	entry = infra_find_ip_ratedata(infra, &rep->client_addr,
+		rep->client_addrlen, 1);
+	if(entry) {
+		struct rate_data* d = (struct rate_data*)entry->data;
+		d->mesh_wait++;
+		lock_rw_unlock(&entry->lock);
+		return;
+	}
+
+	/* Create it */
+	infra_ip_create_ratedata(infra, &rep->client_addr,
+		rep->client_addrlen, timenow, 1);
+}
+
+void infra_wait_limit_dec(struct infra_cache* infra, struct comm_reply* rep,
+	struct config_file* cfg)
+{
+	struct lruhash_entry* entry;
+	if(cfg->wait_limit == 0)
+		return;
+
+	entry = infra_find_ip_ratedata(infra, &rep->client_addr,
+		rep->client_addrlen, 1);
+	if(entry) {
+		struct rate_data* d = (struct rate_data*)entry->data;
+		if(d->mesh_wait > 0)
+			d->mesh_wait--;
+		lock_rw_unlock(&entry->lock);
+	}
+}

programming_language: C
filename: infra.h
change_type: ModificationType.MODIFY
diff: @@ -122,6 +122,10 @@ struct infra_cache {
 	rbtree_type domain_limits;
 	/** hash table with query rates per client ip: ip_rate_key, ip_rate_data */
 	struct slabhash* client_ip_rates;
+	/** tree of addr_tree_node, with wait_limit_netblock_info information */
+	rbtree_type wait_limits_netblock;
+	/** tree of addr_tree_node, with wait_limit_netblock_info information */
+	rbtree_type wait_limits_cookie_netblock;
 };
 
 /** ratelimit, unless overridden by domain_limits, 0 is off */
@@ -184,10 +188,22 @@ struct rate_data {
 	/** what the timestamp is of the qps array members, counter is
 	 * valid for that timestamp.  Usually now and now-1. */
 	time_t timestamp[RATE_WINDOW];
+	/** the number of queries waiting in the mesh */
+	int mesh_wait;
 };
 
 #define ip_rate_data rate_data
 
+/**
+ * Data to store the configuration per netblock for the wait limit
+ */
+struct wait_limit_netblock_info {
+	/** The addr tree node, this must be first. */
+	struct addr_tree_node node;
+	/** the limit on the amount */
+	int limit;
+};
+
 /** infra host cache default hash lookup size */
 #define INFRA_HOST_STARTSIZE 32
 /** bytes per zonename reserved in the hostcache, dnamelen(zonename.com.) */
@@ -474,4 +490,16 @@ void ip_rate_delkeyfunc(void* d, void* arg);
 /* delete data */
 #define ip_rate_deldatafunc rate_deldatafunc
 
+/** See if the IP address can have another reply in the wait limit */
+int infra_wait_limit_allowed(struct infra_cache* infra, struct comm_reply* rep,
+	int cookie_valid, struct config_file* cfg);
+
+/** Increment number of waiting replies for IP */
+void infra_wait_limit_inc(struct infra_cache* infra, struct comm_reply* rep,
+	time_t timenow, struct config_file* cfg);
+
+/** Decrement number of waiting replies for IP */
+void infra_wait_limit_dec(struct infra_cache* infra, struct comm_reply* rep,
+	struct config_file* cfg);
+
 #endif /* SERVICES_CACHE_INFRA_H */

programming_language: C
filename: mesh.c
change_type: ModificationType.MODIFY
diff: @@ -47,6 +47,7 @@
 #include "services/outbound_list.h"
 #include "services/cache/dns.h"
 #include "services/cache/rrset.h"
+#include "services/cache/infra.h"
 #include "util/log.h"
 #include "util/net_help.h"
 #include "util/module.h"
@@ -415,6 +416,14 @@ void mesh_new_client(struct mesh_area* mesh, struct query_info* qinfo,
 	if(rep->c->tcp_req_info) {
 		r_buffer = rep->c->tcp_req_info->spool_buffer;
 	}
+	if(!infra_wait_limit_allowed(mesh->env->infra_cache, rep,
+		edns->cookie_valid, mesh->env->cfg)) {
+		verbose(VERB_ALGO, "Too many queries waiting from the IP. "
+			"dropping incoming query.");
+		comm_point_drop_reply(rep);
+		mesh->stats_dropped++;
+		return;
+	}
 	if(!unique)
 		s = mesh_area_find(mesh, cinfo, qinfo, qflags&(BIT_RD|BIT_CD), 0, 0);
 	/* does this create a new reply state? */
@@ -522,6 +531,8 @@ void mesh_new_client(struct mesh_area* mesh, struct query_info* qinfo,
 		}
 	}
 #endif
+	infra_wait_limit_inc(mesh->env->infra_cache, rep, *mesh->env->now,
+		mesh->env->cfg);
 	/* update statistics */
 	if(was_detached) {
 		log_assert(mesh->num_detached_states > 0);
@@ -953,6 +964,8 @@ mesh_state_cleanup(struct mesh_state* mstate)
 		 * takes no time and also it does not do the mesh accounting */
 		mstate->reply_list = NULL;
 		for(; rep; rep=rep->next) {
+			infra_wait_limit_dec(mesh->env->infra_cache,
+				&rep->query_reply, mesh->env->cfg);
 			comm_point_drop_reply(&rep->query_reply);
 			log_assert(mesh->num_reply_addrs > 0);
 			mesh->num_reply_addrs--;
@@ -1436,6 +1449,8 @@ mesh_send_reply(struct mesh_state* m, int rcode, struct reply_info* rep,
 		comm_point_send_reply(&r->query_reply);
 		m->reply_list = rlist;
 	}
+	infra_wait_limit_dec(m->s.env->infra_cache, &r->query_reply,
+		m->s.env->cfg);
 	/* account */
 	log_assert(m->s.env->mesh->num_reply_addrs > 0);
 	m->s.env->mesh->num_reply_addrs--;
@@ -1491,6 +1506,28 @@ void mesh_query_done(struct mesh_state* mstate)
 		}
 	}
 	for(r = mstate->reply_list; r; r = r->next) {
+		struct timeval old;
+		timeval_subtract(&old, mstate->s.env->now_tv, &r->start_time);
+		if(mstate->s.env->cfg->discard_timeout != 0 &&
+			((int)old.tv_sec)*1000+((int)old.tv_usec)/1000 >
+			mstate->s.env->cfg->discard_timeout) {
+			/* Drop the reply, it is too old */
+			/* briefly set the reply_list to NULL, so that the
+			 * tcp req info cleanup routine that calls the mesh
+			 * to deregister the meshstate for it is not done
+			 * because the list is NULL and also accounting is not
+			 * done there, but instead we do that here. */
+			struct mesh_reply* reply_list = mstate->reply_list;
+			verbose(VERB_ALGO, "drop reply, it is older than discard-timeout");
+			infra_wait_limit_dec(mstate->s.env->infra_cache,
+				&r->query_reply, mstate->s.env->cfg);
+			mstate->reply_list = NULL;
+			comm_point_drop_reply(&r->query_reply);
+			mstate->reply_list = reply_list;
+			mstate->s.env->mesh->stats_dropped++;
+			continue;
+		}
+
 		i++;
 		tv = r->start_time;
 
@@ -1514,6 +1551,8 @@ void mesh_query_done(struct mesh_state* mstate)
 			 * because the list is NULL and also accounting is not
 			 * done there, but instead we do that here. */
 			struct mesh_reply* reply_list = mstate->reply_list;
+			infra_wait_limit_dec(mstate->s.env->infra_cache,
+				&r->query_reply, mstate->s.env->cfg);
 			mstate->reply_list = NULL;
 			comm_point_drop_reply(&r->query_reply);
 			mstate->reply_list = reply_list;
@@ -2046,6 +2085,8 @@ void mesh_state_remove_reply(struct mesh_area* mesh, struct mesh_state* m,
 			/* delete it, but allocated in m region */
 			log_assert(mesh->num_reply_addrs > 0);
 			mesh->num_reply_addrs--;
+			infra_wait_limit_dec(mesh->env->infra_cache,
+				&n->query_reply, mesh->env->cfg);
 
 			/* prev = prev; */
 			n = n->next;
@@ -2186,6 +2227,28 @@ mesh_serve_expired_callback(void* arg)
 		log_dns_msg("Serve expired lookup", &qstate->qinfo, msg->rep);
 
 	for(r = mstate->reply_list; r; r = r->next) {
+		struct timeval old;
+		timeval_subtract(&old, mstate->s.env->now_tv, &r->start_time);
+		if(mstate->s.env->cfg->discard_timeout != 0 &&
+			((int)old.tv_sec)*1000+((int)old.tv_usec)/1000 >
+			mstate->s.env->cfg->discard_timeout) {
+			/* Drop the reply, it is too old */
+			/* briefly set the reply_list to NULL, so that the
+			 * tcp req info cleanup routine that calls the mesh
+			 * to deregister the meshstate for it is not done
+			 * because the list is NULL and also accounting is not
+			 * done there, but instead we do that here. */
+			struct mesh_reply* reply_list = mstate->reply_list;
+			verbose(VERB_ALGO, "drop reply, it is older than discard-timeout");
+			infra_wait_limit_dec(mstate->s.env->infra_cache,
+				&r->query_reply, mstate->s.env->cfg);
+			mstate->reply_list = NULL;
+			comm_point_drop_reply(&r->query_reply);
+			mstate->reply_list = reply_list;
+			mstate->s.env->mesh->stats_dropped++;
+			continue;
+		}
+
 		i++;
 		tv = r->start_time;
 
@@ -2213,6 +2276,8 @@ mesh_serve_expired_callback(void* arg)
 			r, r_buffer, prev, prev_buffer);
 		if(r->query_reply.c->tcp_req_info)
 			tcp_req_info_remove_mesh_state(r->query_reply.c->tcp_req_info, mstate);
+		infra_wait_limit_dec(mstate->s.env->infra_cache,
+			&r->query_reply, mstate->s.env->cfg);
 		prev = r;
 		prev_buffer = r_buffer;
 	}

programming_language: C
filename: cachedb_expired_client_timeout.crpl
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,7 @@ server:
 	; testbound script steps, but also reply within the time.
 	serve-expired-client-timeout: 1200
 	module-config: "cachedb iterator"
+	discard-timeout: 3000
 
 cachedb:
 	backend: "testframe"

programming_language: SQL
filename: cachedb_subnet_expired.crpl
change_type: ModificationType.MODIFY
diff: @@ -14,6 +14,7 @@ server:
 	; store for edns subnet content for modules to the right of it.
 	; this keeps subnet content out of cachedb as global content.
 	module-config: "subnetcache cachedb iterator"
+	discard-timeout: 3000
 
 cachedb:
 	backend: "testframe"

programming_language: Shell
filename: doh_downstream.conf
change_type: ModificationType.MODIFY
diff: @@ -11,6 +11,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 	http-query-buffer-size: 1G
 	http-response-buffer-size: 1G
 	http-max-streams: 200

programming_language: CoffeeScript
filename: doh_downstream_notls.conf
change_type: ModificationType.MODIFY
diff: @@ -11,6 +11,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 	http-query-buffer-size: 1G
 	http-response-buffer-size: 1G
 	http-max-streams: 200

programming_language: CoffeeScript
filename: doh_downstream_post.conf
change_type: ModificationType.MODIFY
diff: @@ -11,6 +11,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 	http-query-buffer-size: 1G
 	http-response-buffer-size: 1G
 	http-max-streams: 200

programming_language: CoffeeScript
filename: fwd_three_service.conf
change_type: ModificationType.MODIFY
diff: @@ -11,6 +11,7 @@ server:
 	num-queries-per-thread: 1024
 	use-syslog: no
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 forward-zone:
 	name: "."
 	forward-addr: "127.0.0.1@@TOPORT@"

programming_language: CoffeeScript
filename: iter_ghost_timewindow.rpl
change_type: ModificationType.MODIFY
diff: @@ -3,6 +3,7 @@ server:
 	target-fetch-policy: "0 0 0 0 0"
 	qname-minimisation: "no"
 	minimal-responses: no
+	discard-timeout: 86400
 
 stub-zone:
 	name: "."

programming_language: Shell
filename: ssl_req_order.conf
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 	ssl-port: @PORT@
 	ssl-service-key: "unbound_server.key"
 	ssl-service-pem: "unbound_server.pem"

programming_language: CoffeeScript
filename: tcp_req_order.conf
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 
 	local-zone: "example.net" static
 	local-data: "www1.example.net. IN A 1.2.3.1"

programming_language: CoffeeScript
filename: tcp_sigpipe.conf
change_type: ModificationType.MODIFY
diff: @@ -1,5 +1,5 @@
 server:
-	verbosity: 2
+	verbosity: 4
 	# num-threads: 1
 	interface: 127.0.0.1
 	port: @PORT@
@@ -9,6 +9,7 @@ server:
 	chroot: ""
 	username: ""
 	do-not-query-localhost: no
+	discard-timeout: 3000  # testns uses sleep=2
 
 forward-zone:
 	name: "."

programming_language: CoffeeScript
filename: config_file.c
change_type: ModificationType.MODIFY
diff: @@ -309,6 +309,11 @@ config_create(void)
 	cfg->minimal_responses = 1;
 	cfg->rrset_roundrobin = 1;
 	cfg->unknown_server_time_limit = 376;
+	cfg->discard_timeout = 1900; /* msec */
+	cfg->wait_limit = 1000;
+	cfg->wait_limit_cookie = 10000;
+	cfg->wait_limit_netblock = NULL;
+	cfg->wait_limit_cookie_netblock = NULL;
 	cfg->max_udp_size = 1232; /* value taken from edns_buffer_size */
 	if(!(cfg->server_key_file = strdup(RUN_DIR"/unbound_server.key")))
 		goto error_exit;
@@ -726,6 +731,9 @@ int config_set_option(struct config_file* cfg, const char* opt,
 	else S_YNO("minimal-responses:", minimal_responses)
 	else S_YNO("rrset-roundrobin:", rrset_roundrobin)
 	else S_NUMBER_OR_ZERO("unknown-server-time-limit:", unknown_server_time_limit)
+	else S_NUMBER_OR_ZERO("discard-timeout:", discard_timeout)
+	else S_NUMBER_OR_ZERO("wait-limit:", wait_limit)
+	else S_NUMBER_OR_ZERO("wait-limit-cookie:", wait_limit_cookie)
 	else S_STRLIST("local-data:", local_data)
 	else S_YNO("unblock-lan-zones:", unblock_lan_zones)
 	else S_YNO("insecure-lan-zones:", insecure_lan_zones)
@@ -1207,6 +1215,11 @@ config_get_option(struct config_file* cfg, const char* opt,
 	else O_YNO(opt, "minimal-responses", minimal_responses)
 	else O_YNO(opt, "rrset-roundrobin", rrset_roundrobin)
 	else O_DEC(opt, "unknown-server-time-limit", unknown_server_time_limit)
+	else O_DEC(opt, "discard-timeout", discard_timeout)
+	else O_DEC(opt, "wait-limit", wait_limit)
+	else O_DEC(opt, "wait-limit-cookie", wait_limit_cookie)
+	else O_LS2(opt, "wait-limit-netblock", wait_limit_netblock)
+	else O_LS2(opt, "wait-limit-cookie-netblock", wait_limit_cookie_netblock)
 #ifdef CLIENT_SUBNET
 	else O_LST(opt, "send-client-subnet", client_subnet)
 	else O_LST(opt, "client-subnet-zone", client_subnet_zone)
@@ -1678,6 +1691,8 @@ config_delete(struct config_file* cfg)
 	config_deltrplstrlist(cfg->interface_tag_actions);
 	config_deltrplstrlist(cfg->interface_tag_datas);
 	config_delstrlist(cfg->control_ifs.first);
+	config_deldblstrlist(cfg->wait_limit_netblock);
+	config_deldblstrlist(cfg->wait_limit_cookie_netblock);
 	free(cfg->server_key_file);
 	free(cfg->server_cert_file);
 	free(cfg->control_key_file);

programming_language: C
filename: config_file.h
change_type: ModificationType.MODIFY
diff: @@ -537,6 +537,21 @@ struct config_file {
 	/* wait time for unknown server in msec */
 	int unknown_server_time_limit;
 
+	/** Wait time to drop recursion replies */
+	int discard_timeout;
+
+	/** Wait limit for number of replies per IP address */
+	int wait_limit;
+
+	/** Wait limit for number of replies per IP address with cookie */
+	int wait_limit_cookie;
+
+	/** wait limit per netblock */
+	struct config_str2list* wait_limit_netblock;
+
+	/** wait limit with cookie per netblock */
+	struct config_str2list* wait_limit_cookie_netblock;
+
 	/* maximum UDP response size */
 	size_t max_udp_size;
 

programming_language: C
filename: configlexer.lex
change_type: ModificationType.MODIFY
diff: @@ -464,6 +464,11 @@ domain-insecure{COLON}		{ YDVAR(1, VAR_DOMAIN_INSECURE) }
 minimal-responses{COLON}	{ YDVAR(1, VAR_MINIMAL_RESPONSES) }
 rrset-roundrobin{COLON}		{ YDVAR(1, VAR_RRSET_ROUNDROBIN) }
 unknown-server-time-limit{COLON} { YDVAR(1, VAR_UNKNOWN_SERVER_TIME_LIMIT) }
+discard-timeout{COLON}		{ YDVAR(1, VAR_DISCARD_TIMEOUT) }
+wait-limit{COLON}		{ YDVAR(1, VAR_WAIT_LIMIT) }
+wait-limit-cookie{COLON}	{ YDVAR(1, VAR_WAIT_LIMIT_COOKIE) }
+wait-limit-netblock{COLON}	{ YDVAR(1, VAR_WAIT_LIMIT_NETBLOCK) }
+wait-limit-cookie-netblock{COLON} { YDVAR(1, VAR_WAIT_LIMIT_COOKIE_NETBLOCK) }
 max-udp-size{COLON}		{ YDVAR(1, VAR_MAX_UDP_SIZE) }
 dns64-prefix{COLON}		{ YDVAR(1, VAR_DNS64_PREFIX) }
 dns64-synthall{COLON}		{ YDVAR(1, VAR_DNS64_SYNTHALL) }

programming_language: C
filename: configparser.y
change_type: ModificationType.MODIFY
diff: @@ -189,6 +189,8 @@ extern struct config_parser_state* cfg_parser;
 %token VAR_ANSWER_COOKIE VAR_COOKIE_SECRET VAR_IP_RATELIMIT_COOKIE
 %token VAR_FORWARD_NO_CACHE VAR_STUB_NO_CACHE VAR_LOG_SERVFAIL VAR_DENY_ANY
 %token VAR_UNKNOWN_SERVER_TIME_LIMIT VAR_LOG_TAG_QUERYREPLY
+%token VAR_DISCARD_TIMEOUT VAR_WAIT_LIMIT VAR_WAIT_LIMIT_COOKIE
+%token VAR_WAIT_LIMIT_NETBLOCK VAR_WAIT_LIMIT_COOKIE_NETBLOCK
 %token VAR_STREAM_WAIT_SIZE VAR_TLS_CIPHERS VAR_TLS_CIPHERSUITES VAR_TLS_USE_SNI
 %token VAR_IPSET VAR_IPSET_NAME_V4 VAR_IPSET_NAME_V6
 %token VAR_TLS_SESSION_TICKET_KEYS VAR_RPZ VAR_TAGS VAR_RPZ_ACTION_OVERRIDE
@@ -327,6 +329,8 @@ content_server: server_num_threads | server_verbosity | server_port |
 	server_fast_server_permil | server_fast_server_num  | server_tls_win_cert |
 	server_tcp_connection_limit | server_log_servfail | server_deny_any |
 	server_unknown_server_time_limit | server_log_tag_queryreply |
+	server_discard_timeout | server_wait_limit | server_wait_limit_cookie |
+	server_wait_limit_netblock | server_wait_limit_cookie_netblock |
 	server_stream_wait_size | server_tls_ciphers |
 	server_tls_ciphersuites | server_tls_session_ticket_keys |
 	server_answer_cookie | server_cookie_secret | server_ip_ratelimit_cookie |
@@ -2377,6 +2381,57 @@ server_unknown_server_time_limit: VAR_UNKNOWN_SERVER_TIME_LIMIT STRING_ARG
 		free($2);
 	}
 	;
+server_discard_timeout: VAR_DISCARD_TIMEOUT STRING_ARG
+	{
+		OUTYY(("P(server_discard_timeout:%s)\n", $2));
+		cfg_parser->cfg->discard_timeout = atoi($2);
+		free($2);
+	}
+	;
+server_wait_limit: VAR_WAIT_LIMIT STRING_ARG
+	{
+		OUTYY(("P(server_wait_limit:%s)\n", $2));
+		cfg_parser->cfg->wait_limit = atoi($2);
+		free($2);
+	}
+	;
+server_wait_limit_cookie: VAR_WAIT_LIMIT_COOKIE STRING_ARG
+	{
+		OUTYY(("P(server_wait_limit_cookie:%s)\n", $2));
+		cfg_parser->cfg->wait_limit_cookie = atoi($2);
+		free($2);
+	}
+	;
+server_wait_limit_netblock: VAR_WAIT_LIMIT_NETBLOCK STRING_ARG STRING_ARG
+	{
+		OUTYY(("P(server_wait_limit_netblock:%s %s)\n", $2, $3));
+		if(atoi($3) == 0 && strcmp($3, "0") != 0) {
+			yyerror("number expected");
+			free($2);
+			free($3);
+		} else {
+			if(!cfg_str2list_insert(&cfg_parser->cfg->
+				wait_limit_netblock, $2, $3))
+				fatal_exit("out of memory adding "
+					"wait-limit-netblock");
+		}
+	}
+	;
+server_wait_limit_cookie_netblock: VAR_WAIT_LIMIT_COOKIE_NETBLOCK STRING_ARG STRING_ARG
+	{
+		OUTYY(("P(server_wait_limit_cookie_netblock:%s %s)\n", $2, $3));
+		if(atoi($3) == 0 && strcmp($3, "0") != 0) {
+			yyerror("number expected");
+			free($2);
+			free($3);
+		} else {
+			if(!cfg_str2list_insert(&cfg_parser->cfg->
+				wait_limit_cookie_netblock, $2, $3))
+				fatal_exit("out of memory adding "
+					"wait-limit-cookie-netblock");
+		}
+	}
+	;
 server_max_udp_size: VAR_MAX_UDP_SIZE STRING_ARG
 	{
 		OUTYY(("P(server_max_udp_size:%s)\n", $2));

programming_language: SQL