CVE-2021-41136

LOWNVD 3.73.7—
EchelonGraph scoreMEDIUM confidence

This low-severity CVE scores 3.7 under NVD CVSS v3. EPSS exploit probability: 1.1%, top 37% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
3.7
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 3.7Exploit: NoneExposed: 0

A fix is available — apply it.

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.

CVSS v3
3.7
EG Score
3.7(medium)
EG Risk
22(Track)
EG Risk 22/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity37% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
62.7%
KEV
Not listed

Published

October 12, 2021

Last Modified

May 27, 2025

References (9)

Vendor Advisories for CVE-2021-41136(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhattfm-rubygem-puma-0:5.6.2-1.el8sat2022-07-05redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
RubyGems(1)
PackageVulnerable rangeFixed inDependents
puma0.8.0 ... 4.3.8 (123 versions)4.3.9—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 51× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 107 total refreshes for this CVE.

  1. 2026-07-23 02:04 UTCEG score recompute
  2. 2026-07-22 22:50 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-41136?
CVE-2021-41136 is a low vulnerability published on October 12, 2021. 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…
When was CVE-2021-41136 disclosed?
CVE-2021-41136 was first published in the National Vulnerability Database on October 12, 2021, with the most recent update on May 27, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-41136 actively exploited?
CVE-2021-41136 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 62.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-41136?
CVE-2021-41136 has a CVSS v3 base score of 3.7 (NVD).
How do I remediate CVE-2021-41136?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-41136, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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