CVE-2024-21647: Puma is a web server for Ruby/Rack applications built for parallelism

This month

MEDIUM 5.9REMOTEUPGRADE

CVE-2024-21647 is a medium-severity flaw (CVSS 5.9) affecting puma. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.0% (top 39%)
CISA exploited list	No
Weakness	CWE-444
Published	2024-01-08
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: puma

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2024-01-08 14:15 UTCPublished CVE record published
2026-06-17 07:09 UTCUpdated Record last modified

puma puma UPGRADE

Affected: < 5.6.8 · >= 6.0.0 and < 6.4.2

Fixed in: 5.6.8, 6.4.2

Safe to downgrade to: a release before 6.0.0

1. Check installed version

apt-cache policy puma || rpm -q puma || puma --version

2. UPGRADE to 5.6.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade puma

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade puma

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 6.0.0 (Debian / Ubuntu)

apt-cache madison puma sudo apt install puma=<VERSION_BEFORE_6.0.0> sudo apt-mark hold puma

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list puma sudo dnf downgrade puma-<VERSION_BEFORE_6.0.0> sudo dnf versionlock add puma

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2024-21647?

puma: upgrade to 5.6.8, 6.4.2. Exact commands for each OS are on this page.

Is CVE-2024-21647 being exploited?

CVE-2024-21647 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2024-21647 affect?

CVE-2024-21647 affects puma. Severity is medium (CVSS 5.9). 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 limi

How urgent is CVE-2024-21647?

Priority 41/100. Remotely exploitable, no login, no user action

Software pages

Ruby vulnerabilities

Related CVEs

CVE-2024-45614 MEDIUM 5.4 UPGRADE Puma is a Ruby/Rack web server built for parallelism
CVE-2023-40175 HIGH 7.3 UPGRADE Puma is a Ruby/Rack web server built for parallelism

References

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