Vulnerability in QPACK prefixed-integer decoder (CVE-2026-100661)
Summary
Vulnerability in QPACK prefixed-integer decoder (CVE-2026-100661). 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 a denial-of-service vulnerability in the QPACK prefixed-integer decoder (QpackUtil.decodePrefixedInteger), which does not bound the number of continuation bytes it will process. A remote, unauthenticated peer can open a QPACK unidirectional stream (type 0x02 encoder or 0x03 decoder) and send a first byte with all prefix bits set (e.g. 0xFF for a 7-bit prefix or 0x3F for a 5-bit prefix) followed by an endless run of 0x80 continuation bytes. The decoder returns -1 ('need more bytes'), so callers never consume the input, the ByteToMessageDecoder cumulator grows without bound, and each decode() invocation re-scans the whole accumulated buffer, yielding O(N^2) CPU cost. The result is unbounded per-connection heap growth (OutOfMemoryError) and event-loop CPU starvation, reachable in every configuration. 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-2026-100661 has been found in QPACK prefixed-integer decoder.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade QPACK prefixed-integer decoder to 4.2.18.Final or later.
If unsure, ask your IT team or search "QPACK prefixed-integer decoder CVE-2026-100661" on the vendor's site.
CVE-2026-100661 (QPACK prefixed-integer 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 prefixed-integer decoder.
Check the vendor advisory for the affected versions of QPACK prefixed-integer 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 prefixed-integer 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 prefixed-integer 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。
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-100661 netty
References
- web github.com
- web vulncheck.com
- web nvd.nist.gov
- web github.com