CVE-2025-58056 — netty-codec-http
Fix: netty/netty@edb55fdCVE-2025-58056 is a security vulnerability in io.netty:netty-codec-http. A fix is available for io.netty:netty-codec-http — see the affected versions and patch details below.
Netty is vulnerable to request smuggling due to incorrect parsing of chunk extensions
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-58056.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
io.netty:netty-codec-http☕io.netty:netty-codec-httpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
A flaw in netty's parsing of chunk extensions in HTTP/1.1 messages with chunked encoding can lead to request smuggling issues with some reverse proxies.
Details
When encountering a newline character (LF) while parsing a chunk extension, netty interprets the newline as the end of the chunk-size line regardless of whether a preceding carriage return (CR) was found. This is in violation of the HTTP 1.1 standard which specifies that the chunk extension is terminated by a CRLF sequence (see the RFC).
This is by itself harmless, but consider an intermediary with a similar parsing flaw: while parsing a chunk extension, the intermediary interprets an LF without a preceding CR as simply part of the chunk extension (this is also in violation of the RFC, because whitespace characters are not allowed in chunk extensions). We can use this discrepancy to construct an HTTP request that the intermediary will interpret as one request but netty will interpret as two (all lines ending with CRLF, notice the LFs in the chunk extension):
POST /one HTTP/1.1
Host: localhost:8080
Transfer-Encoding: chunked
48;\nAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\n0
POST /two HTTP/1.1
Host: localhost:8080
Transfer-Encoding: chunked
0
The intermediary will interpret this as a single request. Once forwarded to netty, netty will interpret it as two separate requests. This is a problem, because attackers can then the intermediary, as well as perform standard request smuggling attacks against other live users (see this Portswigger article).
Impact
This is a request smuggling issue which can be exploited for bypassing front-end access control rules as well as corrupting the responses served to other live clients.
The impact is high, but it only affects setups that use a front-end which:
- Interprets LF characters (without preceding CR) in chunk extensions as part of the chunk extension.
- Forwards chunk extensions without normalization.
Disclosure
- This vulnerability was disclosed on June 18th, 2025 here: https://w4ke.info/2025/06/18/funky-chunks.html
Discussion
Discussion for this vulnerability can be found here:
Credit
- Credit to @JeppW for uncovering this vulnerability.
- Credit to @JLLeitschuh at Socket for coordinating the vulnerability disclosure.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-http | all versions | 4.1.125.Finalio.netty:netty-codec-http:4.1.125.Final |
| ☕Maven | io.netty:netty-codec-http | ≥ 4.2.0.Alpha1&&< 4.2.5.Final | 4.2.5.Finalio.netty:netty-codec-http:4.2.5.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-codec-http to 4.1.125.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-58056 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-58056 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-58056. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This issue is considered Moderate rather than Important because successful exploitation depends on a very specific deployment condition: the presence of an intermediary reverse proxy that both mishandles lone LF characters in chunk extensions and forwards them unmodified to Netty. By itself, Netty’s parsing quirk does…
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-agent-init-rhel9:0.6.0-11 | RHSA-2025:21148 |
| Red Hat AMQ Broker 7.13.2 | netty-codec-http | RHSA-2025:17567 |
| Red Hat build of Apache Camel 4.10.7 for Spring Boot 3.4.10 | netty-codec-http | RHSA-2025:18028 |
| Red Hat Build of Apache Camel 4.10 for Quarkus 3.20 | netty-codec-http | RHSA-2025:18076 |
| Red Hat build of Quarkus 3.15.7 | netty-codec-http | RHSA-2025:17187 |
| Red Hat build of Quarkus 3.20.3 | netty-codec-http | RHSA-2025:17563 |
| Red Hat JBoss Enterprise Application Platform | io.netty/netty-codec-http:4.1.127.Final-redhat-00001 | RHSA-2025:17299 |
| Red Hat JBoss Enterprise Application Platform 8.0.9 | netty-codec-http | RHSA-2025:17318 |
Frequently Asked Questions
Is CVE-2025-58056 in your dependencies?
O3 Security finds CVE-2025-58056 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.