Vulnerability in io.netty:netty-codec-http3 (CVE-2026-48748)
Summary
Vulnerability in io.netty:netty-codec-http3 (CVE-2026-48748). Risk of unauthorized operations or information disclosure. Exploitable via HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY. Mitigation: upgrade to 4.2.15.Final or later.
Original description
The description as published by the source.
Summary
A memory exhaustion vulnerability in the Netty HTTP/3 codec allows the creation of an infinite number of blocked streams, which can cause OOM error.
Details
The vulnerability exists in io.netty.handler.codec.http3.QpackDecoder#shouldWaitForDynamicTableUpdates:
If a client sends a header referencing a table entry that the server hasn't received yet, the server must pause that stream and wait for the missing entry to arrive. To prevent attackers from exhausting resources by intentionally sending missing references, Netty limits the number of streams that can be blocked at the same time.
However, the check is implemented as:
if (blockedStreamsCount == maxBlockedStreams - 1) {
If the server enables QPACK dynamic tables (by setting HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY > 0) but does not explicitly configure HTTP3_SETTINGS_QPACK_BLOCKED_STREAMS, it defaults to 0.
When maxBlockedStreams is 0, the condition evaluates to blockedStreamsCount == -1. Since blockedStreamsCount starts at 0 and only increments, it never equals -1. This bypasses the limit, allowing an attacker to open an infinite number of streams that block indefinitely. Additionally, the QpackDecoder never removes unblocked streams from the blockedStreams map or decrements the counter, meaning the ReadResumptionListener for each blocked stream is kept in memory for the entire lifetime of the connection. This exhausts server memory and crashes the JVM.
Impact
De…
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-2026-48748 has been found in io.netty:netty-codec-http3.
Attackers can target a specific entry point like HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY 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 4.2.15.Final or later.
If unsure, ask your IT team or search "io.netty:netty-codec-http3 CVE-2026-48748" on the vendor's site.
CVE-2026-48748 (io.netty:netty-codec-http3) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY / HTTP3_SETTINGS_QPACK_BLOCKED_STREAMS / maxBlockedStreams / blockedStreamsCount
Patched: 4.2.15.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-770) exists in io.netty:netty-codec-http3. Attackers reach the vulnerable code path via HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY without authentication.
Check the vendor advisory for the affected versions of io.netty:netty-codec-http3. Attack surface: HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY / HTTP3_SETTINGS_QPACK_BLOCKED_STREAMS / maxBlockedStreams / blockedStreamsCount.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 4.2.15.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
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1Identify 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。
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2Apply patch patch
Upgrade io.netty:netty-codec-http3 to 4.2.15.Finalステージング環境で 4.2.15.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。
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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。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-48748 netty
- Ubuntu UBUNTU-CVE-2026-48748 netty