CVE-2019-9515 [High] | Denial of Service in Swiftnio

Some HTTP/2 implementations are vulnerable to a settings flood, potentially leading to a denial of service. The attacker sends a stream of SETTINGS frames to the peer. Since the RFC requires that the peer reply with one acknowledgement per SETTINGS frame, an empty SETTINGS frame is almost equivalent in behavior to a ping. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-29	9.05%	8.89%	-0.15%
2	2026-04-04	10.39%	9.05%	-1.35%
3	2026-02-19	—	10.39%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-29

9.05%

8.89%

-0.15%

2026-04-04

10.39%

9.05%

-1.35%

2026-02-19

—

10.39%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
7.5	3.0	HIGH	`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
7.8	2.0	HIGH	`AV:N/AC:L/Au:N/C:N/I:N/A:C` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:C) Complete availability impact.	10.0	6.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

7.5

3.0

HIGH

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

7.8

2.0

HIGH

AV:N/AC:L/Au:N/C:N/I:N/A:C Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:C): Complete availability impact.

10.0

6.9

[email protected]

OS Trackers for CVE-2019-9515

vendor	priority	summary	link
`alpine`	—	CVE-2019-9515: 4 source package rows (containerd, h2o, nodejs, py3-twisted); 28 state rows across 17 repos (3.10-main, 3.11-main, 3.12-main, 3.17-community, 3.17-main, 3.18-community, 3.18-main, 3.19-community, 3.19-main, 3.20-community, 3.20-main, 3.21-community, 3.21-main, 3.22-community, 3.22-main, edge-community, edge-main); fixed 28, open 0.	https://security.alpinelinux.org/vuln/CVE-2019-9515
`debian`	not yet assigned	CVE-2019-9515 not yet assigned priority: Debian including 2 source packages (h2o, trafficserver), 5 status rows across 3 suites (bookworm, bullseye, sid): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2019-9515
`redhat`	high	—	https://access.redhat.com/security/cve/CVE-2019-9515
`suse`	high	CVE-2019-9515 severity important: SUSE including 125 source package names (MozillaFirefox-68.2.0-78.51.4, MozillaFirefox-branding-SLED-68-21.9.8, …), 299 product×package rows across 29 product lines (SUSE Enterprise Storage 7.1, SUSE Liberty Linux 8, … (29 product lines)): Fixed 233, Known Not Affected 66.	https://www.suse.com/security/cve/CVE-2019-9515/
`ubuntu`	medium	CVE-2019-9515 medium priority: Ubuntu including 7 source packages (golang-google-grpc, grpc, …), 132 status rows across 19 suites (bionic, cosmic, disco, eoan, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 53, ignored 35, released 19, needed 14, DNE 6, needs-triage 5.	https://ubuntu.com/security/CVE-2019-9515

Affected software / configurations for CVE-2019-9515

Vendor	Product	Version	Raw CPE
apple	swiftnio	>= 1.0.0, <= 1.4.0	cpe:2.3:a:apple:swiftnio::::::::
apache	traffic_server	>= 6.0.0, <= 6.2.3	cpe:2.3:a:apache:traffic_server::::::::
apache	traffic_server	>= 7.0.0, <= 7.1.6	cpe:2.3:a:apache:traffic_server::::::::
apache	traffic_server	>= 8.0.0, <= 8.0.3	cpe:2.3:a:apache:traffic_server::::::::
canonical	ubuntu_linux	16.04	cpe:2.3:o:canonical:ubuntu_linux:16.04::::lts:::
canonical	ubuntu_linux	18.04	cpe:2.3:o:canonical:ubuntu_linux:18.04::::lts:::
canonical	ubuntu_linux	19.04	cpe:2.3:o:canonical:ubuntu_linux:19.04:::::::*
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*
debian	debian_linux	10.0	cpe:2.3:o:debian:debian_linux:10.0:::::::*
synology	skynas	—	cpe:2.3:a:synology:skynas:-:::::::*
synology	diskstation_manager	6.2	cpe:2.3:o:synology:diskstation_manager:6.2:::::::*
synology	vs960hd_firmware	—	cpe:2.3:o:synology:vs960hd_firmware:-:::::::*
fedoraproject	fedora	29	cpe:2.3:o:fedoraproject:fedora:29:::::::*
fedoraproject	fedora	30	cpe:2.3:o:fedoraproject:fedora:30:::::::*
opensuse	leap	15.0	cpe:2.3:o:opensuse:leap:15.0:::::::*
opensuse	leap	15.1	cpe:2.3:o:opensuse:leap:15.1:::::::*
redhat	jboss_core_services	1.0	cpe:2.3:a:redhat:jboss_core_services:1.0:::::::*
redhat	jboss_enterprise_application_platform	7.2.0	cpe:2.3:a:redhat:jboss_enterprise_application_platform:7.2.0:::::::*
redhat	jboss_enterprise_application_platform	7.3.0	cpe:2.3:a:redhat:jboss_enterprise_application_platform:7.3.0:::::::*
redhat	openshift_container_platform	4.1	cpe:2.3:a:redhat:openshift_container_platform:4.1:::::::*
redhat	openshift_service_mesh	1.0	cpe:2.3:a:redhat:openshift_service_mesh:1.0:::::::*
redhat	openstack	14	cpe:2.3:a:redhat:openstack:14:::::::*
redhat	quay	3.0.0	cpe:2.3:a:redhat:quay:3.0.0:::::::*
redhat	single_sign-on	7.3	cpe:2.3:a:redhat:single_sign-on:7.3:::::::*
redhat	software_collections	1.0	cpe:2.3:a:redhat:software_collections:1.0:::::::*
redhat	enterprise_linux	8.0	cpe:2.3:o:redhat:enterprise_linux:8.0:::::::*
oracle	graalvm	19.2.0	cpe:2.3:a:oracle:graalvm:19.2.0::::enterprise:::
mcafee	web_gateway	>= 7.7.2.0, < 7.7.2.24	cpe:2.3:a:mcafee:web_gateway::::::::
mcafee	web_gateway	>= 7.8.2.0, < 7.8.2.13	cpe:2.3:a:mcafee:web_gateway::::::::
mcafee	web_gateway	>= 8.1.0, < 8.2.0	cpe:2.3:a:mcafee:web_gateway::::::::
f5	big-ip_local_traffic_manager	>= 11.6.1, < 11.6.5.1	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
f5	big-ip_local_traffic_manager	>= 12.1.0, < 12.1.5.1	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
f5	big-ip_local_traffic_manager	>= 13.1.0, < 13.1.3.2	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
f5	big-ip_local_traffic_manager	>= 14.0.0, < 14.0.1.1	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
f5	big-ip_local_traffic_manager	>= 14.1.0, < 14.1.2.1	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
f5	big-ip_local_traffic_manager	>= 15.0.0, < 15.0.1.1	cpe:2.3:a:f5:big-ip_local_traffic_manager::::::::
nodejs	node.js	>= 8.0.0, <= 8.8.1	cpe:2.3:a:nodejs:node.js:::::-:::*
nodejs	node.js	>= 8.9.0, < 8.16.1	cpe:2.3:a:nodejs:node.js:::::lts:::*
nodejs	node.js	>= 10.0.0, <= 10.12.0	cpe:2.3:a:nodejs:node.js:::::-:::*
nodejs	node.js	>= 10.13.0, < 10.16.3	cpe:2.3:a:nodejs:node.js:::::lts:::*
nodejs	node.js	>= 12.0.0, < 12.8.1	cpe:2.3:a:nodejs:node.js:::::-:::*

References for CVE-2019-9515

URL	Tags
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00031.html	Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00032.html	Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2019/Aug/16	Mailing List Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2766	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2796	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2861	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2925	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2939	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:2955	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:3892	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4018	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4019	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4020	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4021	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4040	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4041	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4042	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4045	Third Party Advisory
https://access.redhat.com/errata/RHSA-2019:4352	Third Party Advisory
https://access.redhat.com/errata/RHSA-2020:0727	Third Party Advisory
https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-002.md	Third Party Advisory
https://kb.cert.org/vuls/id/605641/	Third Party Advisory US Government Resource
https://kc.mcafee.com/corporate/index?page=content&id=SB10296	Third Party Advisory
https://lists.apache.org/thread.html/392108390cef48af647a2e47b7fd5380e050e35ae8d1aa2030254c04%40%3Cusers.trafficserver.apache.org%3E
https://lists.apache.org/thread.html/ad3d01e767199c1aed8033bb6b3f5bf98c011c7c536f07a5d34b3c19%40%3Cannounce.trafficserver.apache.org%3E
https://lists.apache.org/thread.html/bde52309316ae798186d783a5e29f4ad1527f61c9219a289d0eee0a7%40%3Cdev.trafficserver.apache.org%3E
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4ZQGHE3WTYLYAYJEIDJVF2FIGQTAYPMC/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CMNFX5MNYRWWIMO4BTKYQCGUDMHO3AXP/
https://seclists.org/bugtraq/2019/Aug/24	Mailing List Third Party Advisory
https://seclists.org/bugtraq/2019/Aug/43	Mailing List Third Party Advisory
https://seclists.org/bugtraq/2019/Sep/18	Mailing List Third Party Advisory
https://security.netapp.com/advisory/ntap-20190823-0005/	Third Party Advisory
https://support.f5.com/csp/article/K50233772	Third Party Advisory
https://support.f5.com/csp/article/K50233772?utm_source=f5support&amp%3Butm_medium=RSS
https://usn.ubuntu.com/4308-1/	Third Party Advisory
https://www.debian.org/security/2019/dsa-4508	Third Party Advisory
https://www.debian.org/security/2019/dsa-4520	Third Party Advisory
https://www.synology.com/security/advisory/Synology_SA_19_33	Third Party Advisory

URL

CVE-2019-9515 | Some HTTP/2 implementations are vulnerable to a settings flood, potentially leading to a denial of service

Exploit prediction scoring system (EPSS) score for CVE-2019-9515

Common vulnerability scoring system (CVSS) metrics for CVE-2019-9515

Weakness enumeration for CVE-2019-9515

OS Trackers for CVE-2019-9515

Affected software / configurations for CVE-2019-9515

References for CVE-2019-9515