Bug 2541808 (CVE-2026-100660)

Summary: CVE-2026-100660 io.netty/netty-codec-http3: netty-codec-http3: Denial of Service via unbounded QPACK encoder memory retention
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
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Netty's HTTP/3 codec (netty-codec-http3). The HTTP/3 header compression (QPACK) encoder stores per-stream state indefinitely when remote clients do not acknowledge encoded data, as no memory limits are enforced. A remote, unauthenticated attacker can exploit this flaw by issuing sequential requests over a single connection while withholding stream acknowledgment instructions. This causes unbounded memory consumption on the server, ultimately resulting in memory exhaustion and a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-09-26 13:31:46 UTC 
Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.0.Final through 4.2.17.Final retains unbounded per-stream QPACK encoder state. QpackEncoder stores a queue and a dynamic-table index tracker for every encoded field section that references the QPACK dynamic table, keyed by the peer-controlled QUIC stream ID, and these entries are released only when the remote decoder sends a Section Acknowledgment or Stream Cancellation instruction — not when the HTTP/3 stream completes. There is no limit on the number of tracked streams, field sections, or retained bytes. A remote, unauthenticated HTTP/3 client can advertise a non-zero QPACK dynamic-table capacity, acknowledge the table insertion so the server reuses a dynamically indexed response header, and then omit all mandatory Section Acknowledgments while issuing sequential requests over a single QUIC connection, bypassing concurrent-stream limits and causing unbounded heap growth until the server exhausts memory (denial of service). Fixed in 4.2.18.Final.