External risk intelligence

Hazelcast Improper Validation Allows Heap and Memory Reads and Crashing

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-107726

Hazelcast is a data platform typically deployed within internal network segments or clusters to support application backends. While network-reachable within these environments, it is not designed to be directly exposed to the public internet. Access is generally restricted to authorized clients and application services, making direct public internet exposure uncommon in typical deployment patterns.

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A security vulnerability has been identified in Hazelcast, a real-time data platform. This issue could allow unauthorized access to sensitive data, potentially lead to system instability, and in some configurations, enable malicious code execution. The main concern is to confirm if our environment is affected by this type of platform and if so, to what extent.

Unauthorized access to sensitive data.
Critical vulnerability in data platform.
Confirm relevance and exposure.

Attack Path

How an attacker could exploit the issue

An attacker could potentially gain unauthorized access to sensitive information or disrupt operations by connecting to a Hazelcast cluster. This vulnerability allows a malicious client to read data from the cluster members' memory and, in some cases, could lead to memory corruption or even arbitrary code execution.

Attacker can connect to the cluster.
Improper data validation triggers vulnerability.
Risk of data exposure and memory corruption.

Live Threat

Current exploitation, exposure, and threat context

When supported by the advisory, an attacker able to connect to a Hazelcast cluster could gain unauthorized access to sensitive information residing within a cluster member's memory, including off-heap data and JVM process address space. This could also lead to service disruptions through crashes and, in some configurations, potentially impact memory integrity.

Cluster member memory data.
Malicious client connects to cluster.
Information disclosure and service disruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

Teams responsible for Hazelcast, likely application owners and platform or infrastructure teams, must first identify all instances of the affected technology. This is crucial for determining exposure, confirming business criticality, and assigning ownership for remediation. Once these steps are complete, a plan can be developed to address the vulnerability based on the identified risks.

Identify affected Hazelcast deployments.
Verify cluster reachability and business criticality.
Plan remediation with accountable owners.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Hazelcast and how is it used?

Hazelcast is a unified, real-time data platform that combines fast data storage with stream processing. Developers and data architects use it to build distributed applications that require high-speed data access and processing across large, clustered environments. By distributing data across a cluster of servers, it enables low-latency performance for critical business services and application backends.

What does CWE-20 mean for CVE-2026-107726?

CWE-20 refers to improper input validation, which occurs when a system processes untrusted data without sufficient checks. In this CVE, the vulnerability stems from Hazelcast failing to properly validate inputs from a client connecting to a cluster. This weakness allows an attacker to bypass security boundaries, potentially reading sensitive memory contents or forcing the cluster member to crash, and in specific enterprise configurations, leading to code execution.

How does an attacker trigger this vulnerability?

The vulnerability is triggered when a malicious client successfully establishes a connection to a Hazelcast cluster and sends specifically crafted, unvalidated data. It is important to note that this flaw requires network connectivity to the cluster itself; simply having an application interact with the data platform normally does not trigger the bug, provided the client is authorized and the interaction follows expected protocols.

Is my deployment at risk according to Halo Surface Signal?

Halo Surface Signal identifies that Hazelcast is typically deployed within protected internal networks or private cluster segments, not directly on the public internet. While the technical flaw allows network-based access to memory, the risk is often mitigated by the fact that Hazelcast is usually restricted to authorized application services, making direct, untrusted external connections to the cluster uncommon in standard configurations.

What are the first steps to address this CVE?

To address this vulnerability, start by inventorying all running instances of Hazelcast to identify which environments are using versions prior to 5.4.5, 5.5.10, 5.6.1, or 5.7.0. Once you have located the affected deployments, evaluate their network placement and criticality. Your primary remediation goal should be to update these instances to the patched versions provided by the vendor to ensure proper input validation is restored.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.