CVE-2026-42582 Netty: HTTP/3 QPACK literal unbounded allocation
Attackers can cause denial of service in Netty HTTP/3 by sending crafted headers that trigger unbounded memory allocation during decoding.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42582?
CVE-2026-42582 is a high-severity denial of service vulnerability in Netty Netty, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final, when decoding header blocks, the non-Huffman branch of io.netty.handler.codec.http3.QpackDecoder#decodeHuffmanEncodedLiteral may execute new byte[length] for a string literal before verifying that length bytes are actually present in the compressed field section. The wire encoding allows a very large length to be expressed in few bytes. There is no check that length <= in.readableBytes() before new byte[length]. This vulnerability is fixed in 4.2.13.Final.
Which versions are affected by CVE-2026-42582?
2 open source packages ship an affected version, including io.netty:netty-codec-http3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-http3 Maven | From 4.2.0.Final | 4.2.13.Final |
io.netty:netty-codec-http3 Maven | From 4.2.0.Final | 4.2.13.Final |
Products include Netty Netty.
How do I fix CVE-2026-42582?
Upgrade io.netty:netty-codec-http3 to 4.2.13.Final or later.
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-2026-42582 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42582 exists.
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-CH03473, CLEANSTART-2026-CL78657, CLEANSTART-2026-HC86648, DEBIAN-CVE-2026-42582, ECHO-bdc7-f9f5-fd1d, GHSA-2c5c-chwr-9hqw and 4 more.