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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
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 | 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 include 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-IX07149, CLEANSTART-2026-KX41856, CLEANSTART-2026-RW47187, CLSA-2026-1784164029, DEBIAN-CVE-2026-46340, GHSA-5xrh-qmmq-w6ch and 10 more.