CVE-2026-48748: Netty codec http3 Netty HTTP/3 QPACK Blocked Streams Vulnerability

HIGH
Advisory Identifier: GHSA-4grm-h2qv-h6w6
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CVSS 7.5
CWE-770
Published
Advisory Summary

CVE-2026-48748 is a HIGH (CVSS 7.5) netty http/3 qpack blocked streams vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Netty codec http3 libraries in the Maven ecosystem. The issue involves netty http/3 qpack blocked streams memory exhaustion. Remediation is available by upgrading affected packages to version 4.2.15.Final.

CVE-2026-48748 at a Glance

CVE Identifier CVE-2026-48748
GHSA Identifier GHSA-4grm-h2qv-h6w6
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Netty codec http3
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-48748

To remediate this vulnerability, upgrade all affected Netty codec http3 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

io.netty:netty-codec-http3 fixed: 4.2.15.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http3</artifactId>
    <version>4.2.15.Final</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=io.netty

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-48748, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=io.netty

Analyze the terminal output to locate any version of Netty codec http3 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.15.Final), your application is affected.

Note: The mvn dependency:tree -Dincludes=io.netty command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Netty codec http3, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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: ```java 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 Denial of Service. Any server using `netty-codec-http3` with QPACK dynamic tables enabled and maxBlockedStreams defaulting to 0 is impacted.

CVE-2026-48748 Affected Netty codec http3 Versions

1 component(s)
Fixed Versions:
4.2.15.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-codec-http3
maven/io.netty/netty-codec-http3
Maven
≥ 4.2.0.Final
< 4.2.15.Final
4.2.15.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-4grm-h2qv-h6w6
NVD — CVE-2026-48748 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-48748
Security Fix Commit FIX COMMIT
https://github.com/netty/netty/commit/75127cab731ee35068d1f0667bffa188bc332f5d
Netty codec http3 Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-48748
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2488441
Netty codec http3 Source Repository REPOSITORY
https://github.com/netty/netty
Netty codec http3 Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.15.Final
Netty codec http3 Security Information SECURITY
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48748.json

Frequently Asked Questions

What is CVE-2026-48748?
CVE-2026-48748 is a security vulnerability in Netty codec http3 involving Netty HTTP/3 QPACK Blocked Streams Memory Exhaustion under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Netty codec http3 versions are affected?
Affected versions include releases prior to 4.2.15.Final across affected packages: io.netty:netty-codec-http3.
What version fixes CVE-2026-48748?
Upgrading to 4.2.15.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-codec-http3 affected?
Yes, io.netty:netty-codec-http3 is affected in releases prior to 4.2.15.Final. Upgrade your dependency to 4.2.15.Final or later.
What is the CVSS score of CVE-2026-48748?
CVE-2026-48748 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-48748?
CVE-2026-48748 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check Maven dependencies for CVE-2026-48748?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=io.netty'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4grm-h2qv-h6w6",
  "modified" : "2026-08-04T21:50:03Z",
  "published" : "2026-06-15T20:43:13Z",
  "aliases" : [ "CVE-2026-48748" ],
  "summary" : "Netty HTTP/3 QPACK Blocked Streams Memory Exhaustion",
  "details" : "### Summary\nA memory exhaustion vulnerability in the Netty HTTP/3 codec allows the creation of an infinite number of blocked streams, which can cause OOM error.\n\n### Details\nThe vulnerability exists in `io.netty.handler.codec.http3.QpackDecoder#shouldWaitForDynamicTableUpdates`:\n\nIf 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.\n\nHowever, the check is implemented as:\n\n```java\nif (blockedStreamsCount == maxBlockedStreams - 1) {\n```\n\nIf 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.\n\nWhen `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.\n\n### Impact\nDenial of Service. Any server using `netty-codec-http3` with QPACK dynamic tables enabled and maxBlockedStreams defaulting to 0 is impacted.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.15.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.14.Final"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-4grm-h2qv-h6w6"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-48748"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/75127cab731ee35068d1f0667bffa188bc332f5d"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-48748"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2488441"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.15.Final"
  }, {
    "type" : "WEB",
    "url" : "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48748.json"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-15T20:43:13Z",
    "nvd_published_at" : "2026-06-12T16:16:30Z"
  }
}