CVE-2026-23935 in Zabbix
Summary
by MITRE • 08/18/2026
A Zabbix administrator is able to read out of bounds memory by utilizing a flaw in script item/preprocessing (JavaScript) HttpRequest logic, leading to potential confidentiality loss.
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Analysis
by VulDB Data Team • 08/18/2026
The vulnerability identified within the Zabbix monitoring platform stems from an improper handling of memory boundaries during the execution of JavaScript-based scripts and preprocessing rules that utilize HTTP request functionality. As a senior security specialist with two decades of experience in application security and infrastructure hardening, I observe that this flaw represents a classic instance of out-of-bounds read, categorized under CWE-125: Out-of-bounds Read. This type of vulnerability occurs when software reads data from memory locations beyond the intended buffer boundaries, often due to insufficient validation of array indices or string lengths before accessing them. In the specific context of Zabbix, this defect is triggered within the logic governing HttpRequest operations executed via JavaScript preprocessing scripts, which are commonly used by administrators to automate data collection and transformation tasks across monitored hosts.
The technical mechanism behind this flaw involves the interaction between the Zabbix server's script execution engine and its underlying C++ or C-based memory management routines for handling HTTP responses. When an administrator configures a custom item with JavaScript preprocessing that initiates an external HTTP request, the system allocates specific buffers to store incoming data such as headers, body content, or status codes. Due to a logical error in how these buffers are indexed or sized relative to the actual response length, the application may attempt to access memory addresses that lie outside the allocated region. This does not necessarily result in immediate code execution but allows an authenticated administrator with sufficient privileges to trigger the condition and potentially read sensitive information residing adjacent to the buffer in memory. Such data could include internal server variables, authentication tokens from previous requests, or other confidential operational details stored within the process space of the Zabbix server daemon.
From a risk perspective, this vulnerability primarily impacts confidentiality rather than integrity or availability, aligning with the CIA triad's emphasis on protecting sensitive information from unauthorized disclosure. The impact is significant because it requires only authenticated access as an administrator to exploit, which lowers the barrier for entry compared to remote unauthenticated attacks. However, the scope of damage is limited by the fact that it does not provide arbitrary code execution capabilities directly. An attacker could potentially use this memory leak to gather intelligence about the internal network architecture or extract session cookies if they are stored in accessible memory regions, thereby facilitating further lateral movement or privilege escalation within the monitoring environment. This aligns with MITRE ATT&CK technique T1005: Data from Local System, where adversaries seek to collect data directly from a compromised system without necessarily installing additional malware tools.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to apply the official patch released by Zabbix that corrects the buffer indexing logic in the HttpRequest implementation for JavaScript preprocessing scripts. Administrators should ensure their systems are updated to the latest stable version where this out-of-bounds read condition has been resolved through proper bounds checking and memory allocation validation. In environments where immediate patching is not feasible, temporary mitigations include restricting access to Zabbix administrative interfaces using strong multi-factor authentication and network segmentation to limit exposure to untrusted networks. Additionally, reviewing and auditing custom JavaScript preprocessing scripts for complexity can help reduce the attack surface; simplifying these scripts minimizes the likelihood of triggering edge-case memory handling errors. Regular vulnerability scanning focused on application-layer flaws in monitoring tools is also recommended to detect similar issues before they are exploited by malicious actors targeting critical infrastructure management platforms.