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CVE-2026-56816 high CVSS 7.5

Vulnerability in io.netty:netty-codec-http3 (CVE-2026-56816)

Summary

Vulnerability in io.netty:netty-codec-http3 (CVE-2026-56816). Risk of unauthorized operations or information disclosure. Exploitable via payLoadLength. Mitigation: upgrade to 4.2.16.Final or later.

Original description

The description as published by the source.

Summary

Netty's Http3FrameCodec buffers incoming data for HTTP/3 reserved frame types up to the specified payload length without any limits. The payload length is read directly from the wire and trusted without validation. A bad actor can send a reserved frame with a payload length of up to Integer.MAX_VALUE, causing the server to buffer the data in memory. This leads to an OOM and a gradual Denial of Service due to memory exhaustion as multiple streams are opened.

Details

io.netty.handler.codec.http3.Http3FrameCodec#decodeFrame handles reserved frame types as follows:

                // Handling reserved frame types
                // https://tools.ietf.org/html/draft-ietf-quic-http-32#section-7.2.8
                if (in.readableBytes() < payLoadLength) {
                    return 0;
                }

The payLoadLength is read directly from the wire and trusted implicitly. Since payLoadLength can be up to Integer.MAX_VALUE and there is no maximum payload length enforcement for reserved frames, the decoder will accumulate bytes in memory until the wire-provided length is reached.

This allows a bad actor to exhaust server memory by opening multiple QUIC streams and sending reserved frames with large payload lengths, followed by a small amount of data (e.g., up to the defined limit) on each stream.

PoC

    @Test
    public void test() throws Exception {
        EventLoopGroup group = new MultiThreadIoEventLoopGroup(1, NioIoHandler.n…

Source: GitHub Security Advisories (Global) 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-2026-56816 has been found in io.netty:netty-codec-http3.
Attackers can target a specific entry point like payLoadLength over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade io.netty:netty-codec-http3 to 4.2.16.Final or later.
If unsure, ask your IT team or search "io.netty:netty-codec-http3 CVE-2026-56816" on the vendor's site.

CVE-2026-56816 (io.netty:netty-codec-http3) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: payLoadLength
Patched: 4.2.16.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.

❓ What is the problem

A vulnerability (CWE-400) exists in io.netty:netty-codec-http3. Attackers reach the vulnerable code path via payLoadLength without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of io.netty:netty-codec-http3. Attack surface: payLoadLength.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 4.2.16.Final.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

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

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで io.netty:netty-codec-http3 を使っているサービスとバージョンを洗い出す。

  2. 2
    Apply patch patch 
    Upgrade io.netty:netty-codec-http3 to 4.2.16.Final

    ステージング環境で 4.2.16.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。

  3. 3
    Post-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。

Affected packages

maven io.netty:netty-codec-http3
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.2.16.Final"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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