CVE-2026-100724: Software Security Vulnerability Vulnerability

MODERATE
Advisory Identifier: GHSA-9hc9-gcfq-xg98
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CVSS 5.4
CWE-444
Published
Advisory Summary

CVE-2026-100724 is a MODERATE (CVSS 5.4) security vulnerability vulnerability (CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')) affecting Software libraries in the Maven ecosystem. The weakness occurs when the product acts as an intermediary http agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed http requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-100724 at a Glance

CVE Identifier CVE-2026-100724
GHSA Identifier GHSA-9hc9-gcfq-xg98
Severity MODERATE
CVSS v3.1 Base Score 5.4
CWE Classification CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 5.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-100724

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-100724, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling'), where the product acts as an intermediary http agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed http requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

http4k (Maven package org.http4k:http4k-core) before 6.49.0.0, 5.42.0.0 and 4.51.0.0 uses substring (Contains) matching on the Host header by default in reverseProxy() and reverseProxyRouting() when dispatching to configured virtual hosts. If these functions are deployed as a public-facing inbound HTTP handler with two or more configured virtual hosts, a remote attacker can supply a Host header that merely contains a configured vhost name (for example Host: admin.evil.com for a vhost configured as "admin") and be routed to that vhost, bypassing routing-based authorization. The intended outbound-dispatch and test-time uses, where the Host value is set by the calling application, are not affected.

References

GitHub Advisory / Wiki ADVISORY
https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6
NVD — CVE-2026-100724 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-100724
Security Fix Commit FIX COMMIT
https://github.com/http4k/http4k/commit/0121b05537
Security Fix Commit FIX COMMIT
https://github.com/http4k/http4k/commit/54c6385615
www.vulncheck.com/advisories/http4k-b... WEB
https://www.vulncheck.com/advisories/http4k-before-6.49.0.0-host-header-routing-bypass-via-reverseproxy

Frequently Asked Questions

What is CVE-2026-100724?
CVE-2026-100724 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling').
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-100724?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-100724?
CVE-2026-100724 has a CVSS v3.1 base score of 5.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-100724?
CVE-2026-100724 is classified under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.).
How can I check Maven dependencies for CVE-2026-100724?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9hc9-gcfq-xg98",
  "modified" : "2026-09-27T03:31:03Z",
  "published" : "2026-09-27T03:31:03Z",
  "aliases" : [ "CVE-2026-100724" ],
  "details" : "http4k (Maven package org.http4k:http4k-core) before 6.49.0.0, 5.42.0.0 and 4.51.0.0 uses substring (Contains) matching on the Host header by default in reverseProxy() and reverseProxyRouting() when dispatching to configured virtual hosts. If these functions are deployed as a public-facing inbound HTTP handler with two or more configured virtual hosts, a remote attacker can supply a Host header that merely contains a configured vhost name (for example Host: admin.evil.com for a vhost configured as \"admin\") and be routed to that vhost, bypassing routing-based authorization. The intended outbound-dispatch and test-time uses, where the Host value is set by the calling application, are not affected.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-100724"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/commit/0121b05537"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/commit/54c6385615"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/http4k-before-6.49.0.0-host-header-routing-bypass-via-reverseproxy"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-444" ],
    "severity" : "MODERATE",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-27T02:17:20Z"
  }
}