CVE-2020-28466 in nats-server
Summary
by MITRE • 03/07/2021
This affects all versions of package github.com/nats-io/nats-server/server. Untrusted accounts are able to crash the server using configs that represent a service export/import cycles. Disclaimer from the maintainers: Running a NATS service which is exposed to untrusted users presents a heightened risk. Any remote execution flaw or equivalent seriousness, or denial-of-service by unauthenticated users, will lead to prompt releases by the NATS maintainers. Fixes for denial of service issues with no threat of remote execution, when limited to account holders, are likely to just be committed to the main development branch with no special attention. Those who are running such services are encouraged to build regularly from git.
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Analysis
by VulDB Data Team • 03/30/2026
The vulnerability identified as CVE-2020-28466 represents a critical denial-of-service weakness within the NATS messaging system server implementation. This flaw affects all versions of the github.com/nats-io/nats-server/server package and specifically targets the server's handling of untrusted account configurations. The vulnerability arises from insufficient validation of service export/import configurations that can create circular references, allowing malicious actors to craft specific configuration payloads that trigger server crashes. This issue particularly impacts deployments where NATS servers are exposed to untrusted users or external networks, creating a significant security risk for organizations relying on NATS for mission-critical messaging infrastructure.
The technical implementation of this vulnerability stems from the server's failure to properly detect and prevent circular dependency chains in service export and import configurations. When untrusted accounts submit configuration data containing service export/import cycles, the NATS server processes these references without adequate cycle detection mechanisms. This processing leads to infinite loops or stack exhaustion during configuration validation, ultimately causing the server process to crash and become unavailable to legitimate users. The flaw operates at the configuration parsing and validation layer of the server, making it particularly dangerous as it can be triggered through normal account configuration submission processes without requiring elevated privileges or authentication.
The operational impact of CVE-2020-28466 extends beyond simple server unavailability to potentially disrupt entire messaging infrastructures that depend on NATS for communication. Organizations running NATS servers in environments where untrusted users have access to configuration capabilities face immediate risk of service disruption, which could cascade into broader system failures depending on the criticality of the messaging infrastructure. The vulnerability's potential for remote exploitation means that attackers can trigger the denial-of-service condition from external networks without requiring prior authentication, making it particularly dangerous for publicly exposed NATS deployments. This risk is further amplified by the fact that the vulnerability affects all versions of the server package, indicating a fundamental flaw in the configuration validation logic rather than a specific implementation bug.
Security mitigations for this vulnerability require immediate attention from system administrators and security teams managing NATS deployments. The primary defense involves implementing strict access controls to prevent untrusted users from submitting configuration data to NATS servers, particularly in environments where external access is permitted. Organizations should consider deploying NATS servers behind proper authentication and authorization layers, ensuring that only trusted administrators can modify service exports and imports. Additionally, the maintainers have explicitly recommended building from the main development branch regularly, as this provides access to the latest fixes and security improvements. Network segmentation and monitoring solutions should be implemented to detect unusual configuration submission patterns that might indicate exploitation attempts. From a compliance perspective, this vulnerability aligns with CWE-367 weakness category for Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities and represents a significant concern under ATT&CK framework's T1499 technique for network denial-of-service attacks, particularly when considering the potential for cascading failures in distributed systems relying on NATS messaging.