Vulnerability in QPACK encoder-stream instruction decoder (CVE-2026-100662)
Summary
Vulnerability in QPACK encoder-stream instruction decoder (CVE-2026-100662). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 4.2.18.Final or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-100662 has been found in QPACK encoder-stream instruction decoder.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade QPACK encoder-stream instruction decoder to 4.2.18.Final or later.
If unsure, ask your IT team or search "QPACK encoder-stream instruction decoder CVE-2026-100662" on the vendor's site.
CVE-2026-100662 (QPACK encoder-stream instruction decoder) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 4.2.18.Final — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in QPACK encoder-stream instruction decoder.
Check the vendor advisory for the affected versions of QPACK encoder-stream instruction decoder.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 4.2.18.Final.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで QPACK encoder-stream instruction decoder を使っているサービスとバージョンを洗い出す。
-
2Apply patch patch
Upgrade QPACK encoder-stream instruction decoder to 4.2.18.Finalステージング環境で 4.2.18.Final に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
References
- web github.com
- web vulncheck.com
- web nvd.nist.gov
- web github.com