# CVE-2026-46340: Netty: SCTP reassembly nests buffers without bound

> A remote attacker can cause a denial of service in Netty SCTP handlers by sending fragmented messages that create unbounded nested buffer structures.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Jun 2026
- **Updated:** 18 Sep 2026
- **Also known as:** CLEANSTART-2026-IX07149, CLEANSTART-2026-KX41856, CLEANSTART-2026-RW47187, CLSA-2026-1784164029, DEBIAN-CVE-2026-46340, GHSA-5xrh-qmmq-w6ch, MINI-2g5f-79xf-xqcp, MINI-66xh-gc9p-8w39, MINI-9qqq-6j9m-vrh5, MINI-g83f-j9v6-mcgw, MINI-hrc2-2p52-c3vj, MINI-m7g8-398x-w3jm, MINI-pp8j-3qr3-g434, MINI-qh36-8746-66cv, MINI-rf58-9hqj-h44g, UBUNTU-CVE-2026-46340

## What is CVE-2026-46340?

CVE-2026-46340 is a high-severity denial of service vulnerability in Netty Netty, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Netty is a network application framework for development of protocol servers and clients. In versions of netty-transport-sctp prior to 4.1.135.Final and 4.2.15.Final, for each non-complete SctpMessage fragment the handler does `fragments.put(streamId, Unpooled.wrappedBuffer(frag, byteBuf))`, wrapping the previous accumulator and the new slice into a *new* CompositeByteBuf every time. After N fragments the accumulator is an N-deep chain of composites, each holding references and component arrays; readableBytes()/getBytes() on the final buffer recurse N levels. There is no limit on N, on total bytes, or on the number of streamIdentifiers an attacker can open (each gets its own map entry). A peer that never sets the `complete` flag can grow this structure indefinitely from tiny 1-byte DATA chunks. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-46340?

4 open source packages ship an affected version, including io.netty:netty-transport-sctp. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.netty:netty-transport-sctp` | Maven | All versions | 4.1.135.Final |
| `io.netty:netty-transport-sctp` | Maven | All versions | 4.1.135.Final |
| `io.netty:netty-transport-sctp` | Maven | From 4.2.0.Final | 4.2.15.Final |
| `io.netty:netty-transport-sctp` | Maven | From 4.2.0.Final | 4.2.15.Final |

Products: Netty Netty.

## How do I fix CVE-2026-46340?

Upgrade io.netty:netty-transport-sctp to a fixed version for your release line: 4.1.135.Final or 4.2.15.Final.

## Is CVE-2026-46340 being exploited?

There is no known exploitation of CVE-2026-46340 in the wild and no public exploit code.

## Other vulnerabilities in Netty Netty

- [CVE-2026-75595](https://insights.sbomify.com/CVE-2026-75595/): Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext (critical 9.1)
- [CVE-2026-75596](https://insights.sbomify.com/CVE-2026-75596/): Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing (high 8.7)
- [CVE-2026-59901](https://insights.sbomify.com/CVE-2026-59901/): Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang (high 8.7)
- [CVE-2026-55851](https://insights.sbomify.com/CVE-2026-55851/): Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion (high 8.7)
- [CVE-2026-56745](https://insights.sbomify.com/CVE-2026-56745/): Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46340 and fix it if it is affected.

What it is: CVE-2026-46340 is a high-severity denial of service vulnerability in Netty Netty, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-46340 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.netty:netty-transport-sctp (Maven): affected all versions; fixed in 4.1.135.Final
- io.netty:netty-transport-sctp (Maven): affected all versions; fixed in 4.1.135.Final
- io.netty:netty-transport-sctp (Maven): affected from 4.2.0.Final; fixed in 4.2.15.Final
- io.netty:netty-transport-sctp (Maven): affected from 4.2.0.Final; fixed in 4.2.15.Final

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-46340/ (Markdown: https://insights.sbomify.com/CVE-2026-46340/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46340
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46340
- OSV: https://osv.dev/vulnerability/CVE-2026-46340

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46340/
Summaries are generated and may contain mistakes; the official description above is the record.