CVE-2026-23934 in Zabbix
Summary
by MITRE • 08/18/2026
An authenticated user is able to cause disproportionate CPU load on the Frontend webserver by sending specifically crafted requests to the Frontend validate.api.exists action, leading to potential denial of service.
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Analysis
by VulDB Data Team • 08/18/2026
The vulnerability identified involves a resource exhaustion flaw within the frontend validation logic of a web application's API layer. Specifically, an authenticated user can trigger disproportionate CPU consumption on the server hosting the frontend by interacting with the validate.api.exists endpoint. This issue stems from inefficient algorithmic complexity or insufficient input sanitization in the backend processing routine that handles existence checks for specific data entities. When maliciously crafted requests are submitted, the server is forced to perform excessive computational operations relative to the size of the request payload. Unlike unauthenticated attacks which might be mitigated by basic rate limiting at the network edge, this vulnerability exploits valid authentication credentials, allowing attackers who have obtained or compromised legitimate user accounts to bypass initial access controls and directly impact system stability.
From a technical perspective, this flaw represents an inefficient algorithmic complexity issue where the time required to process a request grows disproportionately with the input size. The validate.api.exists action likely performs deep database queries, complex string matching, or recursive checks without adequate optimization or caching mechanisms. When subjected to crafted inputs designed to maximize these computational paths, the server's central processing unit is saturated, leading to thread pool exhaustion and increased latency for all other users sharing that resource. This behavior aligns with CWE-400, which describes Uncontrolled Resource Consumption, as well as CWE-756: Missing or Incorrectly Implemented Cautionary Computational Limit. The attack vector relies on the application's inability to distinguish between legitimate high-load scenarios and malicious exploitation attempts within the validation logic itself.
The operational impact of this vulnerability is significant, primarily manifesting as a Denial of Service condition for authenticated users. Since the attacker must be authenticated, the scope of potential damage is limited to systems where credentials are compromised or shared, but the severity remains critical due to the ease of execution and the direct impact on service availability. The disproportionate CPU load can cause timeouts, dropped connections, and eventual server crashes if not mitigated by upstream infrastructure controls. This degradation affects not only the targeted account's experience but also degrades performance for other tenants in multi-tenant environments or general users relying on the same frontend instance. In severe cases, repeated exploitation could lead to permanent service outages requiring manual intervention to restart services and clear stuck processes.
To mitigate this risk, developers should implement strict input validation and size limits on all parameters passed to the validate.api.exists endpoint. Algorithmic complexity must be reviewed and optimized, potentially by introducing caching layers for frequent existence checks or using more efficient data structures such as hash maps instead of linear searches where applicable. Additionally, implementing application-level rate limiting specific to this API action can prevent rapid-fire requests from overwhelming server resources. It is also advisable to deploy Web Application Firewalls with rules that detect anomalous request patterns indicative of resource exhaustion attacks. For immediate relief, infrastructure-level protections such as CPU throttling or auto-scaling policies should be configured to isolate and terminate processes consuming excessive computational resources before they impact the broader application stack. These measures collectively address both CWE-400 and mitigate the potential for abuse outlined in MITRE ATT&CK technique T1496: Resource Hijacking, ensuring that authenticated users cannot leverage system logic flaws to disrupt service availability.