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Fencer Vulns
medium 6.5

CVE-2025-6442 json

Ruby WEBrick read_header HTTP Request Smuggling Vulnerability

published 2025-06-25 16 mo ago modified 2026-06-17 4 mo ago also GHSA-r995-q44h-hr64 , EUVD-2025-19113

cvss
6.5
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

Ruby WEBrick read_header HTTP Request Smuggling Vulnerability. This vulnerability allows remote attackers to smuggle arbitrary HTTP requests on affected installations of Ruby WEBrick. This issue is exploitable when the product is deployed behind an HTTP proxy that fulfills specific conditions.

The specific flaw exists within the read_headers method. The issue results from the inconsistent parsing of terminators of HTTP headers. An attacker can leverage this vulnerability to smuggle arbitrary HTTP requests. Was ZDI-CAN-21876.

Patch / fix

  • rubygems webrick 1.8.2
  • ruby-lang webrick 1.8.2
  • ruby-webrick Debian 14, Debian 13 1.9.1-1

debian advisories DEBIAN-CVE-2025-6442

  • ruby-webrick Ubuntu 22.04 LTS 1.7.0-3ubuntu0.2
  • ruby-webrick Ubuntu 24.04 LTS 1.8.1-1ubuntu0.2
  • ruby-webrick Ubuntu 26.04 LTS, Ubuntu 25.10 1.9.1-1
  • ruby2.3 Ubuntu Pro 16.04 LTS 2.3.1-2~ubuntu16.04.16+esm11
  • ruby2.5 Ubuntu Pro 18.04 LTS 2.5.1-1ubuntu1.16+esm6
  • ruby2.7 Ubuntu Pro 20.04 LTS 2.7.0-5ubuntu1.18+esm3

ubuntu advisories UBUNTU-CVE-2025-6442

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • ruby2.5 SLE Module for Basesystem 15 SP7 2.5.9-150700.24.3.1
  • ruby2.5 SLE Module for Basesystem 15 SP6, SLE High Performance Computing 15 SP5-ESPOS, SLE High Performance Computing 15 SP4-ESPOS +13 more 2.5.9-150000.4.46.1

suse advisories SUSE-SU-2025:4264-1SUSE-SU-2025:02739-2SUSE-SU-2025:02739-1

  • ruby Azure Linux 3.0 3.3.5-4
  • rubygem-webrick Azure Linux 3.0 1.8.1-2
  • ruby CBL-Mariner 2.0 3.1.7-2
  • rubygem-webrick CBL-Mariner 2.0 1.7.0-2

azure linux advisories AZL-64352AZL-64355AZL-64364AZL-64367

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-6442 updated cvss 6.5

webrick: Ruby WEBrick Request Smuggling Vulnerability

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/fluentd-rhel8, openshift-logging/fluentd-rhel9 Red Hat OpenShift Service Mesh 3 openshift-service-mesh/istio-cni-rhel9, openshift-service-mesh/istio-pilot-rhel9, openshift-service-mesh/istio-proxyv2-rhel9, openshift-service-mesh/istio-rhel9-operator, openshift-service-mesh/istio-must-gather-rhel9, openshift-service-mesh/istio-sail-operator-bundle, +1 more Red Hat 3scale API Management Platform 2 3scale-amp2/zync-rhel8, 3scale-amp2/zync-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 ruby, ruby-ri, ruby-irb, ruby-libs, ruby-rdoc, ruby-tcltk Red Hat Enterprise Linux 7 ruby, ruby-irb, rubygems, ruby-libs, ruby-tcltk, rubygem-json, +6 more Red Hat Enterprise Linux 8 ruby, ruby-irb, rubygems, ruby-libs, rubygem-pg, rubygem-irb, +25 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 pcs, pcs-snmp Red Hat Satellite 6 puppet-agent, rubygem-webrick
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 8 ruby, ruby-irb, rubygems, ruby-libs, rubygem-pg, rubygem-irb, +25 more Red Hat Enterprise Linux 9 ruby, rubygems, ruby-libs, rubygem-irb, rubygem-rbs, rubygem-rss, +13 more Red Hat Enterprise Linux 10 ruby Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
16 mo ago

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.0 6.5 CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
GitHub 3.0 6.5 CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N

Affected packages

ecosystem package affected fixed in
rubygems webrick
<1.8.2
1.8.2

Affected products

  • Ruby WEBrick

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.