CVE-2026-1199 in Zabbix
Summary
by MITRE • 08/18/2026
Zabbix API and Frontend login lockout mechanism has a flaw where several unsuccessful login requests are not properly counted towards the block counter if sent simultaneously, potentially allowing for more password guesses than intended.
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Analysis
by VulDB Data Team • 08/18/2026
The Zabbix monitoring platform contains a critical authentication bypass vulnerability within its API and frontend login mechanisms that undermines the integrity of account lockout policies designed to prevent brute-force attacks. This flaw stems from a race condition in how the system processes concurrent authentication requests, allowing an attacker to circumvent rate limiting controls by sending multiple unsuccessful login attempts simultaneously rather than sequentially. Under normal operational conditions, Zabbix is configured to temporarily block user accounts or IP addresses after a specified number of failed login attempts, serving as a primary defense against automated credential stuffing and dictionary attacks that attempt to guess valid usernames and passwords through high-volume trial-and-error methods.
The technical root cause lies in the lack of atomic operations when updating the counter for failed login attempts within the application database or session storage. When multiple requests arrive at nearly identical timestamps, they may read the current failure count before any single request has incremented it to reflect a new attempt. Consequently, each concurrent request perceives the state as unchanged and proceeds with authentication without triggering the lockout threshold that would have been enforced if the requests were processed one after another in strict sequence. This non-atomic update mechanism creates a window of opportunity where the system fails to accurately track the total volume of malicious activity occurring within a short time frame, effectively nullifying the protective barrier intended by the security configuration.
From an operational impact perspective, this vulnerability significantly lowers the cost and complexity for attackers seeking to compromise Zabbix administrative accounts or user credentials. By leveraging parallelized requests through tools such as curl with multi-threading capabilities or custom scripts utilizing asynchronous HTTP libraries, threat actors can execute hundreds or thousands of password guesses in a fraction of the time it would take under sequential processing. This acceleration increases the likelihood of successfully guessing weak passwords before any manual intervention or automated alerting systems can detect and mitigate the intrusion attempt. The exploitability is further heightened by the fact that Zabbix often manages critical infrastructure monitoring data, making successful authentication highly valuable for lateral movement within a network environment.
This vulnerability aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization, specifically highlighting how race conditions in access control mechanisms can lead to privilege escalation or unauthorized access. Furthermore, it relates to ATT&CK technique T1110.004, known as Brute Force: Password Spraying, where attackers attempt common passwords against many accounts simultaneously, although this specific flaw also facilitates traditional brute-force attacks by removing the time-based constraints that typically slow down such efforts. The failure to properly synchronize state updates across concurrent requests represents a fundamental deviation from secure coding practices required for robust authentication systems.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Administrators should immediately apply vendor-provided patches or updates that resolve this race condition, ensuring that the lockout counter increments atomically using database-level locking mechanisms such as SELECT FOR UPDATE or optimistic concurrency control with version checks. In environments where patching is not immediately feasible, network-layer controls can be implemented to limit the rate of incoming authentication requests per IP address, effectively enforcing the intended security posture at the infrastructure level rather than relying solely on application logic. Additionally, implementing multi-factor authentication adds a critical layer of defense that remains effective regardless of password guessing attempts, as it requires possession of a secondary factor beyond knowledge-based credentials. Regular auditing of login logs and alerting on anomalous spikes in failed authentication events can also help detect exploitation attempts early, allowing for rapid response to potential compromise scenarios.