Netty HTTP/3 QPACK encoder-stream unbounded memory exhaustion DoS
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 1 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-400.
Summary
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 §4.3.3), 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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
Remediation
- Fix · CNA netty (netty) Fixed in 4.2.18.Final
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
netty 4.2.18.Final
7 records Highest priority Priority HIGH 4 HIGH, 2 MEDIUM, 1 LOW
Other records, highest priority first
- TI-2026-64821 Netty 4.2.11 through 4.2.17 QUIC Hostname Verification BypassPriority HIGH 77
- TI-2026-64816 Netty before 4.2.18.Final QpackEncoder Unbounded Memory RetentionPriority HIGH 77
- TI-2026-64819 Netty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3Priority HIGH 71
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat OpenShift Dev Spaces | Affected | No fix yet |
Not affected: 1 product
- Red Hat OpenShift AI (RHOAI)
Timeline
- 2026-10-02 Threatist record created from CVE-2026-100662
- 2026-10-03 Alias added: GHSA-w648-8654-gr82
References
More netty vulnerabilities
- TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
- TI-2026-30861 Netty: HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization CVSS 3.1CRITICAL 9.8
- TI-2026-30864 Netty: HttpClientCodec response desynchronization CVSS 3.1CRITICAL 9.1
- TI-2026-30859 Netty: DNS Codec Input Validation Bypass in Netty (Encoder + Decoder) CVSS 3.1CRITICAL 9.1
- TI-2026-64821 Netty 4.2.11 through 4.2.17 QUIC Hostname Verification Bypass CVSS 4.0HIGH 8.7
- TI-2026-64816 Netty before 4.2.18.Final QpackEncoder Unbounded Memory Retention CVSS 4.0HIGH 8.7
Sources
- CVE-2026-100662 · CVE Program
- CVE-2026-100662 · NVD
- FIRST EPSS
- GHSA-w648-8654-gr82 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-100662 · Red Hat security data · CC BY 4.0
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