CVE-2026-107726 in Hazelcast
Summary
by MITRE • 10/09/2026
Hazelcast is a unified real-time data platform combining stream processing with a fast data store. Prior to 5.4.5, 5.5.10, and 5.6.1, improper validation of data supplied by a malicious client able to connect to a cluster allows arbitrary reads from a cluster member's Java heap, off-heap data, and JVM process address space. The same flaw can crash cluster members and, in some Hazelcast Enterprise Edition configurations, corrupt memory with possible arbitrary code execution. Both slim and full distributions are affected. This issue is fixed in versions 5.4.5, 5.5.10, 5.6.1, and 5.7.0.
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Analysis
by VulDB Data Team • 10/09/2026
Hazelcast serves as a unified real-time data platform that integrates stream processing capabilities with an extremely fast distributed data store, enabling organizations to build scalable applications capable of handling high-throughput workloads. The software architecture relies on cluster members communicating via specific binary protocols to share state and process events in near real time. This design necessitates strict validation of all incoming network traffic to ensure the integrity and security of the underlying Java Virtual Machine environment. When a client connects to a Hazelcast cluster, it initiates interactions that are processed by various internal handlers responsible for deserializing data structures and executing operations on behalf of the connected node.
A critical vulnerability exists within these input validation mechanisms prior versions 5.4.5, 5.5.10, and 5.6.1. The flaw stems from improper validation of data supplied by a malicious client that has successfully established a connection to one of the cluster members. Because Hazelcast trusts authenticated or accessible connections for performance reasons, an attacker who can reach the service port does not need complex authentication bypasses to exploit this issue. Instead, they simply need to craft specific malformed requests that trigger logic errors in how the server processes incoming payloads. This lack of rigorous boundary checking allows data intended for one part of the system to be misinterpreted or accessed beyond its designated memory boundaries.
The operational impact of this vulnerability is severe and multifaceted. The primary consequence is arbitrary read access from a cluster member's Java heap, off-heap direct byte buffers, and even the JVM process address space itself. This means an attacker can extract sensitive information stored in memory, such as encryption keys, session tokens, or proprietary business data held within distributed maps. Beyond confidentiality breaches, the vulnerability poses significant risks to availability and integrity. The malformed inputs can cause cluster members to crash, leading to denial of service conditions that disrupt real-time processing capabilities. In configurations using Hazelcast Enterprise Edition, the memory corruption resulting from these out-of-bounds accesses may lead to arbitrary code execution, fundamentally compromising the security posture of the entire infrastructure by allowing remote attackers to run malicious commands with the privileges of the Java process.
This flaw affects both slim and full distributions of Hazelcast, indicating that the vulnerability is present in the core networking or serialization layers rather than being isolated to specific feature sets. The presence of this issue highlights the risks associated with high-performance data platforms where performance optimizations sometimes reduce strict input sanitization overheads. Attackers can leverage standard network tools to send crafted packets directly to the Hazelcast port, exploiting the gap between expected protocol behavior and actual implementation logic without needing prior knowledge of internal cluster topology beyond basic connectivity requirements.
To mitigate this risk, organizations running affected versions must upgrade immediately to version 5.4.5, 5.5.10, 5.6.1, or preferably the latest stable release such as 5.7.0 where these validation checks have been hardened. For environments that cannot be patched instantly due to operational constraints, network-level controls should be implemented to restrict access to Hazelcast ports exclusively from trusted application servers and internal subnets. Firewalls and security groups must block any external or untrusted IP addresses from reaching the service endpoints. Additionally, enabling authentication mechanisms where available adds a layer of defense by ensuring that only verified clients can initiate connections, thereby reducing the attack surface for this specific class of memory corruption vulnerabilities.
From a classification perspective, this vulnerability aligns with CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write depending on whether the exploit results in data leakage or code execution via heap corruption. It also maps to MITRE ATT&CK techniques involving Memory Manipulation for persistence or credential access, as well as Initial Access through exploitation of application vulnerabilities. The incident underscores the importance of continuous integration testing that includes fuzzing of network protocols used by critical infrastructure components like distributed caches and stream processors.