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CVE Record

CVE-2026-45416: Netty: SNI handler pre-allocates up to 16 MiB from nine attacker bytes

Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, SslClientHelloHandler.decode() reads the 24-bit TLS handshake length and, when the ClientHello does not fit in the first record, eagerly allocates `ctx.alloc().buffer(handshakeLength)` (line 161). The guard at line 140 is `handshakeLength > maxClientHelloLength && maxClientHelloLength != 0`, and the commonly-used SniHandler/AbstractSniHandler constructors (SniHandler(Mapping), SniHandler(AsyncMapping), AbstractSniHandler()) pass maxClientHelloLength=0 and handshakeTimeoutMillis=0, so the length guard is disabled and no timeout is scheduled. A 16 MiB request exceeds the default pooled chunk size and becomes a huge/unpooled allocation performed immediately. The buffer is retained in the handler until the channel closes. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in the Netty networking library lets an unauthenticated attacker trick a server into reserving up to 16 MiB of memory per connection by sending only nine bytes. Repeated connections can exhaust server memory and knock services offline. Many Java-based applications and appliances embed Netty, so exposure is broad even when teams do not use it directly.

Executive priority

Treat as a priority-two patch cycle: no confirmed active exploitation, but a trivial pre-auth denial-of-service against TLS-facing Java services with wide dependency reach. Schedule remediation within the next scheduled maintenance window and expedite for any internet-exposed revenue or customer-facing systems.

Technical view

SslClientHelloHandler.decode() reads the 24-bit TLS handshake length and, when the ClientHello spans records, calls ctx.alloc().buffer(handshakeLength) before validating input. The common SniHandler and AbstractSniHandler constructors default maxClientHelloLength and handshakeTimeoutMillis to 0, disabling both the length guard and timeout. A crafted 16 MiB length triggers a huge unpooled allocation retained until channel close. Fixed in Netty 4.1.135.Final and 4.2.15.Final.

Likely exposure

Any internet-reachable TLS endpoint built on Netty 4.2.0.Final through 4.2.14.Final or 4.1.x below 4.1.135.Final that terminates SNI with default handler settings. This includes many Java microservices, API gateways, reverse proxies, and third-party appliances that embed Netty transitively via Spring, gRPC, Reactor, or Vert.x.

Exploitation context

CVSS 3.1 base 7.5 (AV:N/AC:L/PR:N/UI:N/A:H); pre-authentication, network reachable, low complexity. Not listed in CISA KEV as of the source bundle and no public in-the-wild exploitation is cited. Red Hat has issued multiple errata (RHSA-2026:26017, 26018, 26586, 28573, 34608, 37390), indicating broad downstream impact and vendor urgency.

Researcher notes

Root cause is unbounded resource allocation (CWE-770) in SslClientHelloHandler.decode() line 161, gated by an ineffective check at line 140 when maxClientHelloLength=0. Nine bytes of attacker-controlled handshake header suffice to request a 16 MiB buffer that bypasses the pooled chunk path. Retention until channel close amplifies memory pressure across concurrent sockets. Validate fix by confirming the guard now trips regardless of maxClientHelloLength default, and by handshake timeout being scheduled.

Mitigation direction

  • Upgrade Netty to 4.1.135.Final or 4.2.15.Final on all services and rebuild dependent artifacts.
  • Apply Red Hat RHSA-2026:26017, 26018, 26586, 28573, 34608, and 37390 where applicable.
  • Where upgrade is delayed, set non-zero maxClientHelloLength and handshakeTimeoutMillis on SniHandler constructors.
  • Inventory transitive Netty use via Spring Boot, gRPC, Reactor, and Vert.x builds of materials.
  • Front exposed TLS listeners with a non-Netty terminator or WAF that caps ClientHello size.
  • Contact appliance vendors for patched builds that embed Netty.

Validation and detection

  • Run dependency scans (SCA, Trivy, Grype) for netty-handler and netty-codec versions below the fixed releases.
  • Grep container images and fat JARs for netty-*.jar to catch shaded copies.
  • Query runtime service inventories for JVM services exposing TLS on public interfaces.
  • Confirm patched versions load at startup by inspecting Netty version via JMX or /actuator/info.
  • Monitor heap and direct memory metrics for anomalous allocation spikes during handshake load tests.
  • Verify Red Hat errata are applied via rpm -q or subscription-manager on affected hosts.
Prepared
Confidence
high
Sources
12

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

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cwe · low confidence lookup

CWE-770: Exact CWE lookup

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Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-45416 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
13Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-45416Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: Denial of Service due to eager buffer allocation in TLS handshake
other:Red Hat severity ratingcvssV3_1
  • 2026-06-12T15:01:45.671Z: Reported to Red Hat.
  • 2026-06-12T14:10:05.585Z: 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-770

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

CWE-770 · source CWE mapping

Allocation of Resources Without Limits or Throttling

Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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