Summary
http4k: reverseProxy() defaulted to substring (Contains) matching on Host; tightened to Exact
Workarounds
For deployments that cannot upgrade immediately: wrap your reverseProxy() with a host-allow-list filter that requires an exact match against expected vhost names before delegating.
Impact
reverseProxy() and reverseProxyRouting() matched configured vhosts by substring on the Host header (Contains matcher) by default. The intended use of these functions in http4k is outbound dispatch (e.g. matching AWS service subdomains, per the Contains docstring) and test-time composition of fake backend networks. In either of those contexts the matched Host is set by the calling application, not by an external attacker, so the loose match has no exploit surface.
If, however, reverseProxy() was deployed as a public-facing inbound HTTP handler, which the function technically supports but is not the documented intent, an external attacker could send Host: admin.evil.com and reach a vhost configured as admin, bypassing routing-based authorization.
The Contains matcher's docstring explicitly documented this loose behaviour, but because Contains was the default, callers who never read the matcher docs would still get the loose behaviour.
Who is affected: only deployments using reverseProxy() / reverseProxyRouting() as a public-facing inbound HTTP handler with two or more configured virtual hosts. The intended outbound / test-time usage is unaffected. If you did deploy reverseProxy() inbound and rely on multi-vhost routing for authorization, treat upgrade as urgent.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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| Line | Fixed in | Edition |
|---|---|---|
| v6.x (Community) | 6.49.0.0 | Community |
| v5.x (LTS) | 5.42.0.0 | Enterprise, contact [email protected] (if reverseProxy() is present in your v5.x line) |
| v4.x (LTS) | 4.51.0.0 | Enterprise, contact [email protected] (if reverseProxy() is present in your v4.x line) |
The fix changes the default matcher to Exact. Existing callers that genuinely need substring matching (e.g. AWS subdomain dispatch) must explicitly pass matcher = Contains.
Frequently Asked Questions
- What is GHSA-JRPC-7VXP-69P6? GHSA-JRPC-7VXP-69P6 is a medium-severity security vulnerability in org.http4k:http4k-core (maven), affecting versions >= 6.0.0.0, < 6.48.0.0. It is fixed in 6.49.0.0, 5.42.0.0, 4.51.0.0.
- Which versions of org.http4k:http4k-core are affected by GHSA-JRPC-7VXP-69P6? org.http4k:http4k-core (maven) versions >= 6.0.0.0, < 6.48.0.0 is affected.
- Is there a fix for GHSA-JRPC-7VXP-69P6? Yes. GHSA-JRPC-7VXP-69P6 is fixed in 6.49.0.0, 5.42.0.0, 4.51.0.0. Upgrade to this version or later.
- Is GHSA-JRPC-7VXP-69P6 exploitable, and should I be worried? Whether GHSA-JRPC-7VXP-69P6 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-JRPC-7VXP-69P6 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-JRPC-7VXP-69P6?
- Upgrade
org.http4k:http4k-coreto 6.49.0.0 or later - Upgrade
org.http4k:http4k-coreto 5.42.0.0 or later - Upgrade
org.http4k:http4k-coreto 4.51.0.0 or later
- Upgrade