CVE-2023-40175Public exploitNetwork attack vector

Request smuggling via inconsistent body boundary parsing

Published Aug 18, 2023 · Updated Oct 7, 2024

HTTP request smuggling in Puma before 5.6.7 and 6.0.0 through 6.3.0 allows remote attackers to inject requests via malformed HTTP bodies. In lib/puma/client.rb, setup_body accepts an empty Content-Length as valid, while decode_chunk retains trailer bytes as the next pipelined request. Exploitation requires conflicting message-boundary interpretation on a shared connection; injected requests are processed by the hosted Rack application.

CVSS severity9.8
Critical
EPSS probability0.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Puma before 5.6.7 and 6.0.0 through 6.3.0 allows remote attackers to inject requests via malformed HTTP bodies. In lib/puma/client.rb, setup_body accepts an empty Content-Length as valid, while decode_chunk retains trailer bytes as the next pipelined request. Exploitation requires conflicting message-boundary interpretation on a shared connection; injected requests are processed by the hosted Rack application.

The record

CVE
CVE-2023-40175
Published
Aug 18, 2023
Updated
Oct 7, 2024
Vendor
Puma
Product
Puma
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 18, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <5.6.7
  2. Affected versionversion=< 5.6.7
  3. Affected versionversion=>= 6.0.0, < 6.3.1
  4. Affected versionversion=6.0.0 <6.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Puma · Pumaversion=0 <5.6.7; version=< 5.6.7; version=>= 6.0.0, < 6.3.1; version=6.0.0 <6.3.1

Published CVSS scores

9.8GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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