Skip to content
Noroxi
NVD / CVE Program· CNA GitHub_M

CVE-2021-41136: Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') in puma

LowCVSS 3.7 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 14/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 1.2% (FIRST EPSS); higher than 68.6% of all records.
  • Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. A user must open a link or visit a page. Special conditions such as timing or configuration are required.
  • Fixed version: puma (Debian:10) 3.12.0-2+deb10u3; puma (Debian:11) 4.3.8-1+deb11u2; puma (Debian:12) 5.5.2-1.

Low priority for now. Upgrade to puma (Debian:10) 3.12.0-2+deb10u3; puma (Debian:11) 4.3.8-1+deb11u2; puma (Debian:12) 5.5.2-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Puma is a HTTP 1.1 server for Ruby/Rack applications. Prior to versions 5.5.1 and 4.3.9, using `puma` with a proxy which forwards HTTP header values which contain the LF character could allow HTTP request smugggling. A client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client. The only proxy which has this behavior, as far as the Puma team is aware of, is Apache Traffic Server. If the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request's body. Puma, however, would see it as two requests, and when processing the second request, send back a response that the proxy does not expect. If the proxy has reused the persistent connection to Puma to send another request for a different client, the second response from the first client will be sent to the second client. This vulnerability was patched in Puma 5.5.1 and 4.3.9. As a workaround, do not use Apache Traffic Server with `puma`.

Published
Oct 12, 2021
Updated
Jun 17, 2026
EPSS
1.2% · 68th percentile

Report tools

JSON

Action score

14

Monitor

Low priority for now.

CVSS
14 / 40 · 3.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 1.2%

CNA vs NVD score

NVD
3.7
CNA · GitHub_M
3.7
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-41136

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits every 10 minutes on paid plans, on the hour on the free plan.

Your free account also gets you

  • CVE alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools, at most 30 a day (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every MondayDon't want an account? RSS feed for puma records
Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
pumapuma
debiandebian linux

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • puma puma

    • >= 5.0.0, < 5.5.1, < 4.3.9affected
Affected versions · NVD (4)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • debian debian linux11.0
  • puma pumaup to 4.3.8 inclusive
  • puma puma5.0.0 and later · up to 5.5.0 inclusive

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:10pumabefore 3.12.0-2+deb10u33.12.0-2+deb10u3
Debian:11pumabefore 4.3.8-1+deb11u24.3.8-1+deb11u2
Debian:12pumabefore 5.5.2-15.5.2-1
openSUSE:Leap 15.3rubygem-pumabefore 4.3.11-150000.3.6.24.3.11-150000.3.6.2
openSUSE:Tumbleweedruby3.2-rubygem-puma-5before 5.6.5-1.75.6.5-1.7
openSUSE:Tumbleweedrubygem-puma-4before 4.3.10-1.14.3.10-1.1
openSUSE:Tumbleweedrubygem-puma-5before 5.6.8-1.15.6.8-1.1
openSUSE:Tumbleweedrubygem-puma-5before 5.6.5-1.15.6.5-1.1
Red Hat:satellite_capsule:6.11::el7foremanbefore 0:3.1.1.21-2.el7sat0:3.1.1.21-2.el7sat
Red Hat:satellite_capsule:6.11::el7libsolvbefore 0:0.7.22-1.el7pc0:0.7.22-1.el7pc
Red Hat:satellite_capsule:6.11::el7satellitebefore 0:6.11.0-2.el7sat0:6.11.0-2.el7sat
Red Hat:satellite_capsule:6.11::el8foremanbefore 0:3.1.1.21-2.el8sat0:3.1.1.21-2.el8sat
Red Hat:satellite_capsule:6.11::el8libsolvbefore 0:0.7.22-1.el8pc0:0.7.22-1.el8pc
Red Hat:satellite_capsule:6.11::el8python-djangobefore 0:3.2.13-1.el8pc0:3.2.13-1.el8pc
Red Hat:satellite_capsule:6.11::el8python-lxmlbefore 0:4.7.1-1.el8pc0:4.7.1-1.el8pc
Red Hat:satellite_capsule:6.11::el8python-sqlparsebefore 0:0.4.2-2.el8pc0:0.4.2-2.el8pc
Red Hat:satellite_capsule:6.11::el8python38-djangobefore 0:3.2.13-1.el8pc0:3.2.13-1.el8pc
Red Hat:satellite_capsule:6.11::el8satellitebefore 0:6.11.0-2.el8sat0:6.11.0-2.el8sat
Red Hat:satellite:6.11::el7candlepinbefore 0:4.1.13-1.el7sat0:4.1.13-1.el7sat
Red Hat:satellite:6.11::el7tfm-rubygem-actionpackbefore 0:6.0.4.7-1.el7sat0:6.0.4.7-1.el7sat
Red Hat:satellite:6.11::el7tfm-rubygem-pumabefore 0:5.6.2-1.el7sat0:5.6.2-1.el7sat
Red Hat:satellite:6.11::el7tfm-rubygem-puma-debuginfobefore 0:5.6.2-1.el7sat0:5.6.2-1.el7sat
Red Hat:satellite:6.11::el7tfm-rubygem-sidekiqbefore 0:5.2.10-1.el7sat0:5.2.10-1.el7sat
Red Hat:satellite:6.11::el8candlepinbefore 0:4.1.13-1.el8sat0:4.1.13-1.el8sat

+70

Same product

puma: all records

Other highest-scoring records for the same primary product.

Published before and after this one in the same product

  • ← EarlierCVE-2020-11076May 22, 2020 · HTTP Smuggling via Transfer-Encoding Header in Puma
    31Monitor
  • ← EarlierCVE-2021-29509May 11, 2021 · Keepalive Connections Causing Denial Of Service in puma
    30Monitor
  • Later →CVE-2022-23634Feb 11, 2022 · Information Exposure when using Puma with Rails
    24Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:puma5.5.2-1 · Debian:12Package registry (OSV)
opensuse:ruby3.2-rubygem-puma-55.6.5-1.7 · openSUSE:TumbleweedPackage registry (OSV)
opensuse:rubygem-puma4.3.11-150000.3.6.2 · openSUSE:Leap 15.3Package registry (OSV)
opensuse:rubygem-puma-44.3.10-1.1 · openSUSE:TumbleweedPackage registry (OSV)
opensuse:rubygem-puma-55.6.5-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:candlepin0:4.1.13-1.el7sat · Red Hat:satellite:6.11::el7Package registry (OSV)
red hat:foreman0:3.1.1.21-2.el7sat · Red Hat:satellite_capsule:6.11::el7Package registry (OSV)
red hat:libsolv0:0.7.22-1.el7pc · Red Hat:satellite_capsule:6.11::el7Package registry (OSV)
red hat:python-django0:3.2.13-1.el8pc · Red Hat:satellite_capsule:6.11::el8Package registry (OSV)
red hat:python-lxml0:4.7.1-1.el8pc · Red Hat:satellite_capsule:6.11::el8Package registry (OSV)
red hat:python-sqlparse0:0.4.2-2.el8pc · Red Hat:satellite_capsule:6.11::el8Package registry (OSV)
red hat:python38-django0:3.2.13-1.el8pc · Red Hat:satellite_capsule:6.11::el8Package registry (OSV)
red hat:rubygem-puma0:5.6.2-1.el8sat · Red Hat:satellite:6.11::el8Package registry (OSV)
red hat:satellite0:6.11.0-2.el7sat · Red Hat:satellite_capsule:6.11::el7Package registry (OSV)
red hat:tfm-rubygem-actionpack0:6.0.4.7-1.el7sat · Red Hat:satellite:6.11::el7Package registry (OSV)
red hat:tfm-rubygem-puma0:5.6.2-1.el7sat · Red Hat:satellite:6.11::el7Package registry (OSV)
red hat:tfm-rubygem-sidekiq0:5.2.10-1.el7sat · Red Hat:satellite:6.11::el7Package registry (OSV)
rocky linux:libdb0:5.3.28-42.el8_4 · Rocky Linux:8Package registry (OSV)
RubyGems:puma4.3.9Package registry (OSV)
RubyGems:puma5.5.1Package registry (OSV)
suse:ardana-ansible8.0+git.1632499354.a56668f-3.82.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:ardana-monasca8.0+git.1627997000.6c3bc04-3.30.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-installation8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-operations8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-opsconsole8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-planning8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-security8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:documentation-hpe-helion-openstack-user8.20210806-1.35.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:openstack-ec2-api5.0.1~dev12-4.9.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)
suse:openstack-heat-templates0.0.0+git.1628179051.7d761bf-3.24.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)

+3

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • A user must open a link or visit a page.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
low · data can be read
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
Required
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-444 · Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records