CVE-2024-21647 | HTTP Request/Response Smuggling in puma

Puma is a web server for Ruby/Rack applications built for parallelism. Prior to version 6.4.2, puma exhibited incorrect behavior when parsing chunked transfer encoding bodies in a way that allowed HTTP request smuggling. Fixed versions limits the size of chunk extensions. Without this limit, an attacker could cause unbounded resource (CPU, network bandwidth) consumption. This vulnerability has been fixed in versions 6.4.2 and 5.6.8.

Published: 2024-01-08 Last update: 2025-11-03 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2024-21647 is rated Moderate Risk (53.1/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 2.46%). 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-2024-21647

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 2026-03-06 2.67% 2.46% -0.20%
2 2026-01-26 1.98% 2.67% +0.68%
3 2025-12-01 — 1.98% —

Full EPSS history (21 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2024-21647

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
 2.2 3.6 [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]

Weakness enumeration for CVE-2024-21647

GitHub Security Advisory for CVE-2024-21647

GHSA-c2f4-cvqm-65w2 · Severity: medium · Ecosystem: rubygems — Puma HTTP Request/Response Smuggling vulnerability

OS Trackers for CVE-2024-21647

vendor priority summary link
debian not yet assigned CVE-2024-21647 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-2024-21647
redhat high — https://access.redhat.com/security/cve/CVE-2024-21647
suse medium — https://www.suse.com/security/cve/CVE-2024-21647/
ubuntu medium CVE-2024-21647 medium priority: Ubuntu including 1 source packages (puma), 12 status rows across 12 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 4, released 4, ignored 3, needs-triage 1. https://ubuntu.com/security/CVE-2024-21647

Affected software / configurations for CVE-2024-21647

Vendor Product Version Raw CPE
puma puma < 5.6.8 cpe:2.3:a:puma:puma:*:*:*:*:*:ruby:*:*
puma puma >= 6.0.0, < 6.4.2 cpe:2.3:a:puma:puma:*:*:*:*:*:ruby:*:*

References for CVE-2024-21647

cvelogic Threat Intelligence