Local Information Disclosure Vulnerability in Netty on Unix-Like systems
Impact
When netty's multipart decoders are used local information disclosure can occur via the local system temporary directory if temporary storing uploads on the disk is enabled.
The CVSSv3.1 score of this vulnerability is calculated to be a 6.2/10
Vulnerability Details
On unix-like systems, the temporary directory is shared between all user. As such, writing to this directory using APIs that do not explicitly set the file/directory permissions can lead to information disclosure. Of note, this does not impact modern MacOS Operating Systems.
The method File.createTempFile on unix-like systems creates a random file, but, by default will create this file with the permissions -rw-r--r--. Thus, if sensitive information is written to this file, other local users can read this information.
This is the case in netty's AbstractDiskHttpData is vulnerable.
https://github.com/netty/netty/blob/e5951d46fc89db507ba7d2968d2ede26378f0b04/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractDiskHttpData.java#L80-L101
AbstractDiskHttpData is used as a part of the DefaultHttpDataFactory class which is used by HttpPostRequestDecoder / HttpPostMultiPartRequestDecoder.
You may be affected by this vulnerability your project contains the following code patterns:
channelPipeline.addLast(new HttpPostRequestDecoder(...));
channelPipeline.addLast(new HttpPostMultiPartRequestDecoder(...));
Patches
This has been patched in version 4.1.59.Final.
Workarounds
Specify your own java.io.tmpdir when you start the JVM or use DefaultHttpDataFactory.setBaseDir(...) to set the directory to something that is only readable by the current user.
References
Similar Vulnerabilities
Similar, but not the same.
For more information
If you have any questions or comments about this advisory:
Original Report
Hi Netty Security Team,
I've been working on some security research leveraging custom CodeQL queries to detect local information disclosure vulnerabilities in java applications. This was the result from running this query against the netty project:
https://lgtm.com/query/7723301787255288599/
Netty contains three local information disclosure vulnerabilities, so far as I can tell.
One is here, where the private key for the certificate is written to a temporary file.
https://github.com/netty/netty/blob/e5951d46fc89db507ba7d2968d2ede26378f0b04/handler/src/main/java/io/netty/handler/ssl/util/SelfSignedCertificate.java#L316-L346
One is here, where the certificate is written to a temporary file.
https://github.com/netty/netty/blob/e5951d46fc89db507ba7d2968d2ede26378f0b04/handler/src/main/java/io/netty/handler/ssl/util/SelfSignedCertificate.java#L348-L371
The final one is here, where the 'AbstractDiskHttpData' creates a temporary file if the getBaseDirectory() method returns null. I believe that 'AbstractDiskHttpData' is used as a part of the file upload support? If this is the case, any files uploaded would be similarly vulnerable.
https://github.com/netty/netty/blob/e5951d46fc89db507ba7d2968d2ede26378f0b04/codec-http/src/main/java/io/netty/handler/codec/http/multipart/AbstractDiskHttpData.java#L91
All of these vulnerabilities exist because File.createTempFile(String, String) will create a temporary file in the system temporary directory if the 'java.io.tmpdir' system property is not explicitly set. It is my understanding that when java creates a file, by default, and using this method, the permissions on that file utilize the umask. In a majority of cases, this means that the file that java creates has the permissions: -rw-r--r--, thus, any other local user on that system can read the contents of that file.
Impacted OS:
- Any OS where the system temporary directory is shared between multiple users. This is not the case for MacOS or Windows.
Mitigation.
Moving to the Files API instead will fix this vulnerability.
https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#createTempFile-java.nio.file.Path-java.lang.String-java.lang.String-java.nio.file.attribute.FileAttribute...-
This API will explicitly set the posix file permissions to something safe, by default.
I recently disclosed a similar vulnerability in JUnit 4:
https://github.com/junit-team/junit4/security/advisories/GHSA-269g-pwp5-87pp
If you're also curious, this vulnerability in Jetty was also mine, also involving temporary directories, but is not the same vulnerability as in this case.
https://github.com/eclipse/jetty.project/security/advisories/GHSA-g3wg-6mcf-8jj6
I would appreciate it if we could perform disclosure of this vulnerability leveraging the GitHub security advisories feature here. GitHub has a nice credit system that I appreciate, plus the disclosures, as you can see from the sampling above, end up looking very nice.
https://github.com/netty/netty/security/advisories
This vulnerability disclosure follows Google's 90-day vulnerability disclosure policy (I'm not an employee of Google, I just like their policy). Full disclosure will occur either at the end of the 90-day deadline or whenever a patch is made widely available, whichever occurs first.
Cheers,
Jonathan Leitschuh
Latest trending attack
Criticalyesterday
Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)
This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it.
Why a second control
CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution.
Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library.
The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support.
What this control checks
Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service.
How to read the result
Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside.
This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification.
Affected and fixed versions
Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution.
Recommendations
Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library.
Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli.
Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.
