CVE-2019-16770 | Potential DOS attack in Puma

In Puma before versions 3.12.2 and 4.3.1, a poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack. If more keepalive connections to Puma are opened than there are threads available, additional connections will wait permanently if the attacker sends requests frequently enough. This vulnerability is patched in Puma 4.3.1 and 3.12.2.

Published: 2019-12-05 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2019-16770 is rated Moderate Risk (48.6/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.93%). Review affected assets and schedule 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-2019-16770

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 1.59% 1.93% +0.35%
2 2026-03-04 1.10% 1.59% +0.49%
3 2026-03-01 — 1.10% —

Full EPSS history (36 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-16770

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L 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:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]
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]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P 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:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2019-16770

GitHub Security Advisory for CVE-2019-16770

GHSA-7xx3-m584-x994 · Severity: medium · Ecosystem: rubygems — A poorly-behaved client could use keepalive requests to monopolize Puma's reactor and create a denial of service attack

OS Trackers for CVE-2019-16770

vendor priority summary link
debian not yet assigned CVE-2019-16770 not yet assigned priority: Debian including 1 source packages (puma), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2019-16770
redhat medium — https://access.redhat.com/security/cve/CVE-2019-16770
suse high CVE-2019-16770 severity important: SUSE including 377 source package names (ardana-ansible-9.0+git.1581611758.f694f7d-3.16.1, ardana-cinder-8.0+git.1579279939.ee7da88-3.39.3, …), 759 product×package rows across 29 product lines (HPE Helion OpenStack 8, SUSE Linux Enterprise High Availability Extension 15, … (29 product lines)): Fixed 751, Known Not Affected 8. https://www.suse.com/security/cve/CVE-2019-16770/
ubuntu medium CVE-2019-16770 medium priority: Ubuntu including 1 source packages (puma), 7 status rows across 7 suites (bionic, disco, eoan, focal, trusty, upstream, xenial): DNE 3, ignored 2, needs-triage 1, not-affected 1. https://ubuntu.com/security/CVE-2019-16770

Affected software / configurations for CVE-2019-16770

Vendor Product Version Raw CPE
puma puma >= 3.0.0, < 3.12.2 cpe:2.3:a:puma:puma:*:*:*:*:*:ruby:*:*
puma puma >= 4.0.0, < 4.3.1 cpe:2.3:a:puma:puma:*:*:*:*:*:ruby:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

References for CVE-2019-16770

cvelogic Threat Intelligence