IO.UNDERTOW:UNDERTOW-CORE · CVE-2026-28368 · Package
FIX → 2.2.40.Final · 2.3.25.Final
Undertow parses some HTTP header names differently from upstream proxies, so a crafted request can be read one way by the proxy and another way by Undertow. An attacker can use this to bypass security controls and reach resources they should not access.
first public Mar 27, 2026 · 2 sources
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Applications that run Undertow as the HTTP server behind a proxy, load balancer or gateway that parses headers itself are the exposed case. Standalone Undertow with no proxy in front still parses the same headers, so the version check matters there too. Teams on a version outside the affected ranges can skip it.
A flaw was found in Undertow. This vulnerability allows a remote attacker to construct specially crafted requests where header names are parsed differently by Undertow compared to upstream proxies. This discrepancy in header interpretation can be exploited to launch request smuggling attacks, potentially bypassing security controls and accessing unauthorized resources.
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Not affected if no-proxy-in-front, version-outside-affected-range
Who cares cwe-444, java, jboss, maven, undertow, wildfly
io.undertow:undertow-core in your Maven dependency tree (for example with mvn dependency:tree).Upgrade to 2.2.40.Final · 2.3.25.Final
io.undertow:undertow-core 2.2.40.Final for the 2.2.x lineio.undertow:undertow-core 2.3.25.Final for the 2.3.x lineGitHub Advisory Database, CC-BY 4.0 · NVD data is provided by NIST and is public domain. Posts quoted belong to their authors.