CVE-2026-23930 in Zabbix
Summary
by MITRE • 08/18/2026
An unauthenticated user is able to cause disproportionate CPU load on the Frontend webserver by sending specifically crafted requests to the Frontend popup.testtriggerexpr action, leading to potential denial of service.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified involves a critical resource exhaustion flaw within the frontend component of the application architecture, specifically targeting the popup.testtriggerexpr endpoint. This issue stems from an unauthenticated attack vector that allows any external actor with network access to trigger disproportionate CPU utilization on the web server hosting this service. The core technical deficiency lies in the lack of sufficient input validation and rate limiting mechanisms associated with this specific action handler. When a specially crafted request is transmitted, the backend logic processes it through complex or recursive operations without adequate safeguards against maliciously constructed payloads. This results in an inefficient execution path that consumes significantly more computational resources than intended for standard user interactions, effectively turning a simple HTTP request into a high-cost operation for the server infrastructure.
From a technical perspective, this flaw represents a classic instance of algorithmic complexity abuse or resource exhaustion due to improper input handling. The attacker can exploit this by sending requests designed to trigger deep recursion, excessive string manipulation, or complex regular expression evaluations that are not bounded by time limits or depth constraints. This behavior aligns with CWE-400, which describes Uncontrolled Resource Consumption, and more specifically CWE-787, Out-of-bounds Write if memory corruption is involved in the processing of these crafted inputs. The absence of authentication requirements for this endpoint exacerbates the severity, as it removes any barrier to entry for potential attackers, allowing them to launch attacks from multiple sources simultaneously without needing valid credentials or session tokens.
The operational impact of this vulnerability is severe, primarily manifesting as a Denial of Service condition against the frontend web server. By sustaining high CPU loads through repeated exploitation attempts, an adversary can degrade the performance of all other services running on the same infrastructure. This leads to increased latency for legitimate users, potential timeouts in API responses, and ultimately complete unavailability of the service if the resource consumption reaches critical thresholds. In a distributed environment, this single point of failure could cascade into broader system instability, affecting downstream microservices that depend on timely responses from the frontend layer. The impact extends beyond mere downtime to include increased operational costs due to auto-scaling triggers being activated unnecessarily and potential data integrity risks if concurrent processing limits are breached during high-load scenarios.
Mitigation strategies must focus on implementing robust input validation and strict rate limiting policies at both the application and network levels. Developers should audit the codebase for the popup.testtriggerexpr action to ensure that all inputs are sanitized and processed with bounded complexity, avoiding recursive calls or expensive operations without depth limits. Implementing Web Application Firewall rules can help detect and block patterns associated with this specific exploit before they reach the application logic. Additionally, enforcing authentication requirements on sensitive endpoints is crucial; if unauthenticated access is not strictly necessary for public functionality, it should be restricted to authenticated users only. Rate limiting based on IP address or user session ID will further mitigate the risk by preventing a single source from overwhelming the server with rapid-fire requests. Regular security testing and code reviews are essential to identify similar patterns in other parts of the application that may share this architectural weakness.