CVE-2026-100656: Netty HttpServerCodec Unbounded Queue Growth via HTTP/1.1 Pipelining
Netty (io.netty:netty-codec-http) contains an unbounded per-connection queue growth flaw in HttpServerCodec. The codec tracks the HTTP method of each still-unanswered pipelined request; the first 32 entries are bit-packed into a single long, but every additional entry is appended to methodOverflowQueue, an ArrayDeque with no size limit and no rejection path. A remote, unauthenticated attacker who pipelines HTTP/1.1 requests on a single connection while withholding reads on their own end (preventing responses from being flushed) can grow this queue without bound, causing unbounded heap growth and denial of service. Affected versions are 4.2.0.Final through 4.2.17.Final and all releases up to and including 4.1.137.Final; the issue is fixed in 4.2.18.Final and 4.1.138.Final.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
io.netty:netty-codec-httpto a version that resolves this vulnerability.Fixed in 4.2.18.Final - Upgrade
Upgrade
io.netty:netty-codec-httpto a version that resolves this vulnerability.Fixed in 4.1.138.Final
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using io.netty:netty-codec-http versions 4.2.0.Final through 4.2.17.Final, or any release up to and including 4.1.137.Final, are affected when HttpServerCodec processes HTTP/1.1 connections.
What must an attacker do to trigger the denial of service?
An unauthenticated remote attacker must send pipelined HTTP/1.1 requests over a single connection and withhold reading responses. This prevents responses from being flushed and allows the per-connection method queue to grow without bound.
Is authentication or user interaction required for exploitation?
No. The issue is network-reachable with low attack complexity and requires neither privileges nor user interaction.
What is the remediation?
Upgrade to Netty 4.2.18.Final or 4.1.138.Final, which contain the fix.