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CVE-2026-55831 high CVSS 7.5

Vulnerability in io.netty:netty-codec-http (CVE-2026-55831)

Summary

Vulnerability in io.netty:netty-codec-http (CVE-2026-55831). Risk of unauthorized operations or information disclosure. Exploitable via DefaultSpdySettingsFrame. Mitigation: upgrade to 4.1.136.Final or later.

Original description

The description as published by the source.

Summary

Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in DefaultSpdySettingsFrame without an implementation-level count cap. A remote SPDY/3.1 peer can send one syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries, amplifying network input into heap growth and ordered-map insertion work.

Details

Inbound SPDY bytes enter SpdyFrameCodec.decode() and are passed directly to the frame decoder. The decoder reads the peer-controlled flags and 24-bit frame length from the common header, then accepts SETTINGS frames with only length >= 4. For SETTINGS payloads, it reads the peer-controlled numSettings field and validates only that the remaining payload is divisible into 8-byte entries and exactly matches that count. Each accepted entry then supplies an attacker-controlled 24-bit ID and value, and the normal delegate path forwards it into spdySettingsFrame.setValue(). The sink is DefaultSpdySettingsFrame: it backs settings with a TreeMap, checks only that IDs fit the SPDY 24-bit maximum, and inserts a new Setting for each previously unseen ID. There is no count budget between the wire-format count validation and the TreeMap insertion site.

PoC

poc.zip

run with

bash ./poc/run.sh

expected output:

NETTY_SPDY_SETTINGS_COUNT_MAP_TRIGGERED settings…

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-2026-55831 has been found in io.netty:netty-codec-http.
Attackers can target a specific entry point like DefaultSpdySettingsFrame 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-http to 4.1.136.Final or later.
If unsure, ask your IT team or search "io.netty:netty-codec-http CVE-2026-55831" on the vendor's site.

CVE-2026-55831 (io.netty:netty-codec-http) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: DefaultSpdySettingsFrame / numSettings / TreeMap / Setting
Patched: 4.1.136.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-http. Attackers reach the vulnerable code path via DefaultSpdySettingsFrame without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of io.netty:netty-codec-http. Attack surface: DefaultSpdySettingsFrame / numSettings / TreeMap / Setting.

🔥 Severity

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

🔧 How to fix

Update to 4.1.136.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-http 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-http to 4.1.136.Final

    ステージング環境で 4.1.136.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-http
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.1.136.Final"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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