CVE-2025-67735: Netty codec http Netty Has A CRLF Injection Vulnerability

MODERATE
Advisory Identifier: GHSA-84h7-rjj3-6jx4
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CVSS 6.5
CWE-93
Published
Advisory Summary

CVE-2025-67735 is a MODERATE (CVSS 6.5) netty has a crlf injection vulnerability (CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')) affecting Netty codec http libraries in the Maven ecosystem. The issue involves netty has a crlf injection vulnerability in io.netty.handler.codec.http.httprequestencoder. Remediation is available by upgrading affected packages to version 4.2.8.Final, 4.1.129.Final.

CVE-2025-67735 at a Glance

CVE Identifier CVE-2025-67735
GHSA Identifier GHSA-84h7-rjj3-6jx4
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')
Affected Product Netty codec http
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.5

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

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

How to Fix CVE-2025-67735

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

io.netty:netty-codec-http fixed: 4.2.8.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.2.8.Final</version>
</dependency>
io.netty:netty-codec-http fixed: 4.1.129.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.1.129.Final</version>
</dependency>
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 -Dincludes=io.netty

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2025-67735, 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 codec http in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.8.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-93: Improper Neutralization of CRLF Sequences ('CRLF Injection'), where the product uses crlf (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes crlf sequences from inputs. In Netty codec http, 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

### Summary The `io.netty.handler.codec.http.HttpRequestEncoder` CRLF injection with the request uri when constructing a request. This leads to request smuggling when `HttpRequestEncoder` is used without proper sanitization of the uri. ### Details The `HttpRequestEncoder` simply UTF8 encodes the `uri` without sanitization (`buf.writeByte(SP).writeCharSequence(uriCharSequence, CharsetUtil.UTF_8);`) The default implementation of HTTP headers guards against such possibility already with a validator making it impossible with headers. ### PoC Simple reproducer: ```java public static void main(String[] args) { EmbeddedChannel client = new EmbeddedChannel(); client.pipeline().addLast(new HttpClientCodec()); EmbeddedChannel server = new EmbeddedChannel(); server.pipeline().addLast(new HttpServerCodec()); server.pipeline().addLast(new ChannelInboundHandlerAdapter() { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { System.out.println("Processing msg " + msg); } }); DefaultHttpRequest request = new DefaultHttpRequest( HttpVersion.HTTP_1_1, HttpMethod.GET, "/s1 HTTP/1.1\r\n" + "\r\n" + "POST /s2 HTTP/1.1\r\n" + "content-length: 11\r\n\r\n" + "Hello World" + "GET /s1" ); client.writeAndFlush(request); ByteBuf tmp; while ((tmp = client.readOutbound()) != null) { server.writeInbound(tmp); } } ``` ### Impact Any application / framework using `HttpRequestEncoder` can be subject to be abused to perform request smuggling using CRLF injection.

CVE-2025-67735 Affected Netty codec http Versions

2 component(s)
Fixed Versions:
4.2.8.Final4.1.129.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
≥ 4.2.0.Alpha1
< 4.2.8.Final
4.2.8.Final
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
< 4.1.129.Final
4.1.129.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4
NVD — CVE-2025-67735 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-67735
Security Fix Commit FIX COMMIT
https://github.com/netty/netty/commit/77e81f1e5944d98b3acf887d3aa443b252752e94
Netty codec http Source Repository REPOSITORY
https://github.com/netty/netty

Frequently Asked Questions

What is CVE-2025-67735?
CVE-2025-67735 is a security vulnerability in Netty codec http involving Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder under CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection').
Which Netty codec http versions are affected?
Affected versions include releases prior to 4.2.8.Final, 4.1.129.Final across affected packages: io.netty:netty-codec-http.
What version fixes CVE-2025-67735?
Upgrading to 4.2.8.Final, 4.1.129.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-codec-http affected?
Yes, io.netty:netty-codec-http is affected in releases prior to 4.2.8.Final, 4.1.129.Final. Upgrade your dependency to 4.2.8.Final, 4.1.129.Final or later.
What is the CVSS score of CVE-2025-67735?
CVE-2025-67735 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2025-67735?
CVE-2025-67735 is classified under CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') (The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.).
How can I check Maven dependencies for CVE-2025-67735?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=io.netty'. 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-84h7-rjj3-6jx4",
  "modified" : "2025-12-20T02:30:14Z",
  "published" : "2025-12-15T23:28:49Z",
  "aliases" : [ "CVE-2025-67735" ],
  "summary" : "Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder",
  "details" : "### Summary\n\nThe `io.netty.handler.codec.http.HttpRequestEncoder` CRLF injection with the request uri when constructing a request. This leads to request smuggling when `HttpRequestEncoder` is used without proper sanitization of the uri.\n\n### Details\n\nThe `HttpRequestEncoder` simply UTF8 encodes the `uri` without sanitization (`buf.writeByte(SP).writeCharSequence(uriCharSequence, CharsetUtil.UTF_8);`)\n\nThe default implementation of HTTP headers guards against such possibility already with a validator making it impossible with headers.\n\n### PoC\n\nSimple reproducer:\n\n```java\npublic static void main(String[] args) {\n\n  EmbeddedChannel client = new EmbeddedChannel();\n  client.pipeline().addLast(new HttpClientCodec());\n\n  EmbeddedChannel server = new EmbeddedChannel();\n  server.pipeline().addLast(new HttpServerCodec());\n  server.pipeline().addLast(new ChannelInboundHandlerAdapter() {\n    @Override\n    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {\n      System.out.println(\"Processing msg \" + msg);\n    }\n  });\n\n  DefaultHttpRequest request = new DefaultHttpRequest(\n    HttpVersion.HTTP_1_1,\n    HttpMethod.GET,\n    \"/s1 HTTP/1.1\\r\\n\" +\n      \"\\r\\n\" +\n      \"POST /s2 HTTP/1.1\\r\\n\" +\n      \"content-length: 11\\r\\n\\r\\n\" +\n      \"Hello World\" +\n      \"GET /s1\"\n  );\n  client.writeAndFlush(request);\n  ByteBuf tmp;\n  while ((tmp = client.readOutbound()) != null) {\n    server.writeInbound(tmp);\n  }\n}\n```\n\n### Impact\n\nAny application / framework using `HttpRequestEncoder` can be subject to be abused to perform request smuggling using CRLF injection.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Alpha1"
      }, {
        "fixed" : "4.2.8.Final"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.129.Final"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-67735"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/77e81f1e5944d98b3acf887d3aa443b252752e94"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-93" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-15T23:28:49Z",
    "nvd_published_at" : "2025-12-16T01:15:52Z"
  }
}