CVE-2025-6442Network attack vector

Request smuggling via permissive header terminator parsing

Published Jun 25, 2025 · Updated Jun 25, 2025

HTTP request smuggling in Ruby WEBrick 1.8.1 allows remote attackers to inject requests through a qualifying HTTP proxy. The read_header parser accepts bare LF header terminators and other malformed line endings instead of requiring CRLF, causing proxy and origin parsing to disagree. Exploitation requires a front-end proxy with different terminator handling and permits attacker-controlled requests to be processed as another request.

CVSS severity6.5
Medium
EPSS probability0.47%
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 Ruby WEBrick 1.8.1 allows remote attackers to inject requests through a qualifying HTTP proxy. The read_header parser accepts bare LF header terminators and other malformed line endings instead of requiring CRLF, causing proxy and origin parsing to disagree. Exploitation requires a front-end proxy with different terminator handling and permits attacker-controlled requests to be processed as another request.

The record

CVE
CVE-2025-6442
Published
Jun 25, 2025
Updated
Jun 25, 2025
Vendor
Ruby
Product
WEBrick
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 25, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 25, 2025Record 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=1.8.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Ruby · WEBrickversion=1.8.1

Published CVSS scores

6.5Zero Day InitiativeCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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