CVE-2026-59782: Zabbix Server Information Disclosure Flaw

CVE-2026-59782 Overview

CVE-2026-59782 is an out-of-bounds read vulnerability in the JavaScript preprocessing engine of Zabbix server. The flaw resides in the Duktape JavaScript engine used for item value preprocessing. A limited administrator with access to configure preprocessing scripts can read raw heap memory from the server process. This exposure can disclose data belonging to other preprocessors that the administrator is not authorized to view. The issue is tracked by Zabbix as ZBX-28193 and categorized as [CWE-125] Out-of-Bounds Read.

Critical Impact

An authenticated limited administrator can leak heap memory contents from the Zabbix server process, potentially exposing sensitive preprocessing data belonging to other monitoring workflows.

Affected Products

• Zabbix Server with JavaScript (Duktape) preprocessing enabled
• Deployments where limited administrators can author or modify preprocessing scripts
• Refer to Zabbix Issue Tracker ZBX-28193 for exact affected versions

Discovery Timeline

• 2026-10-05 - CVE-2026-59782 published to NVD
• 2026-10-06 - Last updated in NVD database

Technical Details for CVE-2026-59782

Vulnerability Analysis

Zabbix supports JavaScript-based preprocessing of collected item values through the embedded Duktape engine. Administrators can define scripts that transform metric data before storage. The vulnerability allows a limited administrator to craft preprocessing JavaScript that triggers reads beyond intended buffer boundaries within the Duktape runtime. The resulting memory contents are returned to the administrator through the preprocessing output path. Because preprocessing workers may handle data from multiple items across tenants or host groups, the leaked heap bytes can include values that the requesting administrator lacks permission to see.

Root Cause

The root cause is an out-of-bounds read [CWE-125] in the Duktape integration layer of the Zabbix server. Insufficient bounds checking on buffers referenced from JavaScript preprocessing operations allows memory beyond the intended object to be returned to the script context. The shared process model of the preprocessing manager means adjacent heap regions can hold data from unrelated items.

Attack Vector

Exploitation requires network access to the Zabbix frontend or API and a valid account with high privileges, specifically a limited administrator who can create or edit preprocessing steps. The attacker configures a JavaScript preprocessing step on an item they control, then triggers execution and observes the preprocessing output or logs. No user interaction and no scope change outside the Zabbix server process are required.

No verified exploit code is published. See the Zabbix Issue Tracker ZBX-28193 for vendor technical details.

Detection Methods for CVE-2026-59782

Indicators of Compromise

• Creation or modification of JavaScript preprocessing steps by limited administrator accounts that normally do not author preprocessing logic
• Preprocessing scripts that return unusually long strings, binary-looking data, or content unrelated to the source item
• Repeated preprocessing errors or test executions issued from a single administrator session

Detection Strategies

• Audit Zabbix frontend and API activity for preprocessing.test invocations and item configuration changes by non-superadmin accounts
• Review preprocessing scripts for unusual buffer, Duktape, or typed-array manipulation that would not appear in legitimate metric transforms
• Correlate configuration changes with downstream item value anomalies to flag probable memory disclosure attempts

Monitoring Recommendations

• Enable Zabbix audit logging and forward it to a central analytics platform for long-term retention and query
• Alert on bulk edits of preprocessing steps by individual administrator accounts within short time windows
• Monitor Zabbix server process memory and worker crash counts for anomalies that may accompany out-of-bounds access attempts

How to Mitigate CVE-2026-59782

Immediate Actions Required

• Review Zabbix Issue Tracker ZBX-28193 and apply the fixed Zabbix server release when available
• Inventory all accounts holding the Admin user type and revoke permissions that are not required for operations
• Restrict the set of hosts and items that limited administrators can configure to reduce the preprocessing attack surface

Patch Information

Zabbix tracks the fix under issue ZBX-28193. Consult the Zabbix Issue Tracker ZBX-28193 for the specific patched versions and upgrade guidance. Upgrade affected Zabbix server instances to the vendor-recommended release.

Workarounds

• Disable JavaScript preprocessing on items where it is not required
• Limit the Admin role to trusted operators and prefer the standard User role for monitoring consumers
• Segment Zabbix server tenants so that sensitive data is not processed alongside items editable by lower-trust administrators
• Enable detailed audit logging and review preprocessing script changes on a scheduled cadence

# Review Zabbix audit log for preprocessing-related configuration changes
# (example query against the Zabbix database)
SELECT clock, userid, action, resourcetype, details
FROM auditlog
WHERE resourcetype IN (15, 16)  -- item and item prototype
  AND details LIKE '%preprocessing%'
ORDER BY clock DESC
LIMIT 100;