Bug 2541871 (CVE-2026-100662)

Summary: CVE-2026-100662 io.netty/netty-codec-http3: netty-codec-http3: Denial of Service via unbounded memory allocation in QPACK stream decoder
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
Version: unspecifiedCC: sdawley
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Hardware: All   
OS: Linux   
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A flaw was found in Netty's HTTP/3 codec. A remote, unauthenticated attacker can cause a Denial of Service (DoS) by establishing an HTTP/3 connection and sending stream instructions that declare excessively large field lengths without delivering the complete data. Because the server does not enforce size limits on these instructions, it continuously allocates and retains connection buffers until memory is exhausted, resulting in an application crash.
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Description OSIDB Bzimport 2026-09-26 13:38:19 UTC 
Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.0.Final through 4.2.17.Final contain an uncontrolled resource consumption vulnerability in the QPACK encoder-stream instruction decoder (QpackEncoderHandler, installed on the peer-initiated unidirectional QPACK encoder stream, type 0x02). The handler accepts an attacker-declared string-literal length of up to Integer.MAX_VALUE (~2 GiB) for the Name Length and Value Length fields of the "Insert With Literal Name" instruction (RFC 9204 ยง4.3.3), with no per-instruction or per-literal length cap and no cumulation-size limit; the existing HTTP/3 limits (maxHeaderListSize, maxUnknownFramePayloadLength, DEFAULT_MAX_FIELD_SECTION_SIZE) are not applied to this handler. A remote, unauthenticated peer with an established HTTP/3 connection to a default Netty HTTP/3 server can declare a very large literal length and then trickle fewer bytes than declared, causing the ByteToMessageDecoder MERGE cumulator to retain and grow the per-connection buffer, and ultimately triggering a large byte-array allocation. This leads to unbounded per-connection heap growth and OutOfMemoryError, resulting in denial of service. Fixed in 4.2.18.Final.