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CVE Record

CVE-2026-44249: Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking

Netty is a network application framework for development of protocol servers and clients. In netty-handler prior to versions 4.1.135.Final and 4.2.15.Final, an attacker can bypass IPv6 subnet rules due to an incorrect masking operation in IpSubnetFilterRule.compareTo(). Valid public IP addresses can bypass the restrictions. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

HighCVSS 8.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Netty, a widely used Java networking library, has a flaw in its IPv6 subnet filter that lets attackers slip past IP allow/deny rules. Applications that rely on Netty's IpSubnetFilterRule to block or restrict IPv6 traffic may accept requests from addresses that should have been rejected. Upgraded versions 4.1.135.Final and 4.2.15.Final correct the check.

Executive priority

Treat as a high-priority patch cycle item, not an emergency. Schedule remediation within the next standard maintenance window and prioritize services where Netty subnet filtering enforces access to sensitive internal or admin functionality.

Technical view

A masking error in IpSubnetFilterRule.compareTo() causes incorrect ordering and evaluation of IPv6 subnet rules, allowing valid public IPv6 addresses to bypass filter restrictions. Root causes map to CWE-1287, CWE-284, and CWE-697. Netty 4.1.135.Final and 4.2.15.Final fix the comparator; versions 4.2.0.Final through 4.2.14.Final and all 4.1.x below 4.1.135.Final are affected.

Likely exposure

Any Java service embedding vulnerable Netty and enforcing IPv6-based access control through IpSubnetFilterRule is exposed. This includes many downstream frameworks and Red Hat middleware products shipping Netty. Services on IPv4-only or those not using Netty's subnet filter for authorization decisions face materially lower exposure.

Exploitation context

No KEV listing and no cited proof of active exploitation as of the source bundle. CVSS 8.1 (AV:N/AC:H/PR:N/UI:N) reflects a network-reachable, unauthenticated bypass with elevated attack complexity. Impact depends on what the bypassed filter was protecting; sensitive admin interfaces or internal APIs behind the rule elevate real-world risk.

Researcher notes

The bug is a comparator/masking defect, so filter behavior can appear correct for common cases while failing on specific IPv6 ranges. Focus review on applications that use IpSubnetFilterRule as an authorization boundary rather than logging or telemetry. Confirm whether downstream frameworks (Vert.x, Spring WebFlux/Reactor Netty, Quarkus, gRPC-Java) have published coordinated advisories, since transitive exposure is broad.

Mitigation direction

  • Upgrade netty-handler to 4.1.135.Final or 4.2.15.Final across all services and container images.
  • Apply relevant Red Hat RHSA errata for affected middleware (JBoss EAP, AMQ, Data Grid, etc.).
  • Inventory transitive Netty dependencies via SBOM or dependency scan and rebuild fat JARs.
  • Layer network-level allow-lists (WAF, firewall, service mesh) in front of application filters as defense-in-depth.
  • Consult vendor advisories for any Netty-embedded product not yet patched.

Validation and detection

  • Query dependency manifests for netty-handler versions below the fixed releases.
  • Confirm running processes load only patched Netty JARs after deployment.
  • Review IpSubnetFilterRule configurations to identify IPv6 rules that carried security weight.
  • Test IPv6 access controls with allowed and denied ranges to confirm rules now enforce correctly.
  • Track Red Hat CSAF VEX feed and GHSA-3qp7-7mw8-wx86 for status changes.
Prepared
Confidence
high
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-1287: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · medium confidence lookup

CWE-284: Authorization and privilege behavior lookup

Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-697: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-44249 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
14Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9GitHub_M
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

8.1High
CVSS 3.1 vector shape for CVE-2026-44249Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPnetty-handler: netty-handler: IPv6 subnet rule bypass due to incorrect masking operation
other:Red Hat severity ratingcvssV3_1
  • 2026-06-11T22:02:05.327Z: Reported to Red Hat.
  • 2026-06-11T20:46:14.110Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nettynetty>= 4.2.0.Final, < 4.2.15.Final, < 4.1.135.FinalListed
Weakness

CWE details

CWE-1287CWE-284CWE-697

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-1287 · source CWE mapping

Improper Validation of Specified Type of Input

Improper Validation of Specified Type of Input represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-284 · source CWE mapping

Improper Access Control

Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-697 · source CWE mapping

Incorrect Comparison

Incorrect Comparison represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs