CVE-2019-9518 | Some HTTP/2 implementations are vulnerable to a flood of empty frames, potentially leading to a denial of service

Some HTTP/2 implementations are vulnerable to a flood of empty frames, potentially leading to a denial of service. The attacker sends a stream of frames with an empty payload and without the end-of-stream flag. These frames can be DATA, HEADERS, CONTINUATION and/or PUSH_PROMISE. The peer spends time processing each frame disproportionate to attack bandwidth. This can consume excess CPU.

Published: 2019-08-13 Last update: 2025-01-14 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2019-9518 is rated High Risk (69.2/100): CVSS High severity, with high exploitation likelihood (EPSS 24.82%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +21.18% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2019-9518

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 3.65% 24.82% +21.18%
2 2026-04-04 4.70% 3.65% -1.05%
3 2026-03-13 — 4.70% —

Full EPSS history (65 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-9518

CVSS metrics for this CVE.

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]

Weakness enumeration for CVE-2019-9518

OS Trackers for CVE-2019-9518

vendor priority summary link
alpine — CVE-2019-9518: 1 source package rows (nodejs); 10 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 10, open 0. https://security.alpinelinux.org/vuln/CVE-2019-9518
debian not yet assigned CVE-2019-9518 not yet assigned priority: Debian including 1 source packages (trafficserver), 3 status rows across 3 suites (bookworm, bullseye, sid): resolved 3. https://security-tracker.debian.org/tracker/CVE-2019-9518
redhat high — https://access.redhat.com/security/cve/CVE-2019-9518
suse high CVE-2019-9518 severity important: SUSE including 98 source package names (MozillaFirefox-68.2.0-78.51.4, MozillaFirefox-branding-SLED-68-21.9.8, …), 304 product×package rows across 30 product lines (SUSE CaaS Platform 4.5, SUSE Enterprise Storage 4, … (30 product lines)): Fixed 213, Known Not Affected 91. https://www.suse.com/security/cve/CVE-2019-9518/
ubuntu medium CVE-2019-9518 medium priority: Ubuntu including 2 source packages (netty, trafficserver), 34 status rows across 18 suites (bionic, disco, eoan, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 16, not-affected 13, released 3, DNE 1, needed 1. https://ubuntu.com/security/CVE-2019-9518

Affected software / configurations for CVE-2019-9518

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_service_mesh 1.0 cpe:2.3:a:redhat:openshift_service_mesh:1.0:*:*:*:*:*:*:*
redhat quay 3.0.0 cpe:2.3:a:redhat:quay:3.0.0:*:*:*:*:*:*:*
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:*:*:*:*:*:*:*:*
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-2019-9518

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-2019:2925 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-2019:4352 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/091b518265bce56a16af87b77c8cfacda902a02079e866f9fdf13b61%40%3Cusers.trafficserver.apache.org%3E
https://lists.apache.org/thread.html/2653c56545573b528f3f6352a29eccaf498bd6fb2a6a59568d81a61d%40%3Cannounce.trafficserver.apache.org%3E
https://lists.apache.org/thread.html/9317fd092b257a0815434b116a8af8daea6e920b6673f4fd5583d5fe%40%3Ccommits.druid.apache.org%3E
https://lists.apache.org/thread.html/ff5b0821a6985159a832ff6d1a4bd311ac07ecc7db1e2d8bab619107%40%3Cdev.trafficserver.apache.org%3E
https://lists.apache.org/thread.html/r99a625fb17032646d96cd23dec49603ff630e9318e44a686d63046bc%40%3Ccommits.cassandra.apache.org%3E
https://lists.apache.org/thread.html/rd31230d01fa6aad18bdadc0720acd1747e53690bd35f73a48e7a9b75%40%3Ccommits.cassandra.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/Sep/18 Mailing List Third Party Advisory
https://security.netapp.com/advisory/ntap-20190823-0005/ Third Party Advisory
https://support.f5.com/csp/article/K46011592 Third Party Advisory
https://support.f5.com/csp/article/K46011592?utm_source=f5support&amp%3Butm_medium=RSS
https://www.debian.org/security/2019/dsa-4520 Third Party Advisory
https://www.synology.com/security/advisory/Synology_SA_19_33 Third Party Advisory
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