Netty HTTP/3 QPACK Blocked Streams Memory Exhaustion

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-48748: 0.39% estimated exploitation activity in the next 30 days; percentile 33.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 the server enables QPACK dynamic tables (by setting HTTP3SETTINGSQPACKMAXTABLECAPACITY 0) but does not explicitly configure HTTP3SETTINGSQPACKBLOCKEDSTREAMS, 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…

Published by the source

15 Jun 2026, 20:43 UTC

Last modified by the source

4 Aug 2026, 21:50 UTC

Source last checked

26 Oct 2026, 16:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-4grm-h2qv-h6w6

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# Patch Next advisory brief: CVE-2026-48748

Advisory: Netty HTTP/3 QPACK Blocked Streams Memory Exhaustion
IDs: CVE-2026-48748, GHSA-4grm-h2qv-h6w6
Record: https://patchnext.com/advisories/cve-2026-48748 (revision 1, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-codec-http3 4.2.15.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-codec-http3: affected >= 4.2.0.Final, <= 4.2.14.Final; fixed in 4.2.15.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-codec-http3: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-codec-http3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-4grm-h2qv-h6w6 (GitHub-reviewed advisory GHSA-4grm-h2qv-h6w6 lists affected ranges: Maven io.netty:netty-codec-http3 >=4.2.0.Final <=4.2.14.Final)

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