### SummaryAn unsafe reading of environment file could potentially cause a denial of service in Netty.When loaded on an Windows application, Netty attemps to load a file that does not exist. If an attacker creates such a large file, the Netty application crash.### DetailsWhen the library netty is loaded in a java windows application, the library tries to identify the system environnement in which it is executed.At this stage, Netty tries to load both `/etc/os-release` and `/usr/lib/os-release` even though it is in a Windows environment.

If netty finds this files, it reads them and loads them into memory.By default :- The JVM maximum memory size is set to 1 GB,- A non-privileged user can create a directory at `C:\` and create files within it.

the source code identified :https://github.com/netty/netty/blob/4.1/common/src/main/java/io/netty/util/internal/PlatformDependent.javaDespite the implementation of the function `normalizeOs()` the source code not verify the OS before reading `C:\etc\os-release` and `C:\usr\lib\os-release`.### PoCCreate a file larger than 1 GB of data in `C:\etc\os-release` or `C:\usr\lib\os-release` on a Windows environnement and start your Netty application.To observe what the application does with the file, the security analyst used "Process Monitor" from the "Windows SysInternals" suite. (https://learn.microsoft.com/en-us/sysinternals/)```cd C:\etcfsutil file createnew os-release 3000000000```

The source code used is the Netty website code example : [Echo ‐ the very basic client and server](https://netty.io/4.1/xref/io/netty/example/echo/package-summary.html).The vulnerability was tested on the 4.1.112.Final version.The security analyst tried the same technique for `C:\proc\sys\net\core\somaxconn` with a lot of values to impact Netty but the only things that works is the "larger than 1 GB file" technique. https://github.com/netty/netty/blob/c0fdb8e9f8f256990e902fcfffbbe10754d0f3dd/common/src/main/java/io/netty/util/NetUtil.java#L186### ImpactBy loading the "file larger than 1 GB" into the memory, the Netty library exceeds the JVM memory limit and causes a crash in the java Windows application.This behaviour occurs 100% of the time in both Server mode and Client mode if the large file exists.Client mode :

Server mode :

somaxconn :

### Severity- Attack vector : "Local" because the attacker needs to be on the system where the Netty application is running.- Attack complexity : "Low" because the attacker only need to create a massive file (regardless of its contents).- Privileges required : "Low" because the attacker requires a user account to exploit the vulnerability.- User intercation : "None" because the administrator don't need to accidentally click anywhere to trigger the vulnerability. Furthermore, the exploitation works with defaults windows/AD settings.- Scope : "Unchanged" because only Netty is affected by the vulnerability.- Confidentiality : "None" because no data is exposed through exploiting the vulnerability.- Integrity : "None" because the explotation of the vulnerability does not allow editing, deleting or adding data elsewhere.- Availability : "High" because the exploitation of this vulnerability crashes the entire java application.