CVE-2025-64529 is a vulnerability classified under CWE-770 (Allocation of Resources Without Limits or Throttling) affecting authzed's SpiceDB, an open-source database designed for managing application permissions. The flaw exists in versions prior to 1.45.2 when users employ the exclusion operator in their authorization schema and configure the server with the `--write-relationships-max-updates-per-call` parameter set above 6500. Under these conditions, if a WriteRelationships API call includes a large number of updates causing the payload size to exceed datastore limits, the server erroneously returns a successful response even though the write operation fails internally. This discrepancy leads to incorrect permission check results, particularly when the failed relationships are involved in resolving relations with exclusions. The root cause is the lack of proper throttling or limits on resource allocation during write operations, causing the system to misreport the state of relationship writes. The vulnerability does not require authentication or user interaction, and the attack vector is network-based with low complexity. The issue was addressed in SpiceDB version 1.45.2 by implementing appropriate limits and error handling. As a temporary mitigation, reducing the `--write-relationships-max-updates-per-call` setting to 1000 limits the size of write operations, preventing the failure condition. No public exploits or active exploitation have been reported to date.

For European organizations, this vulnerability could lead to incorrect permission enforcement in applications relying on SpiceDB for authorization management. Specifically, failed writes that are incorrectly reported as successful may cause the system to grant or deny access improperly, undermining the confidentiality and integrity of sensitive data. This could affect compliance with data protection regulations such as GDPR if unauthorized access occurs. Although the CVSS score is low, the impact on security-critical applications could be significant depending on how extensively the exclusion operator and large write operations are used. Availability is not directly impacted, but trust in the authorization system's correctness may be compromised. Organizations using SpiceDB in cloud-native or microservices environments where dynamic permission changes are frequent are at higher risk. The lack of known exploits reduces immediate threat but does not eliminate risk, especially if attackers discover ways to trigger the failure condition remotely.

European organizations should upgrade all SpiceDB instances to version 1.45.2 or later to apply the official patch addressing this vulnerability. If immediate upgrade is not feasible, configure the server to set `--write-relationships-max-updates-per-call` to 1000 or lower to prevent oversized write operations that trigger the issue. Review authorization schemas to minimize or carefully audit the use of the exclusion operator, especially in conjunction with large batch writes. Implement monitoring and alerting on WriteRelationships API calls to detect anomalously large payloads or unexpected permission check results. Conduct thorough testing of permission enforcement after upgrades or configuration changes to ensure correctness. Additionally, limit network exposure of SpiceDB servers to trusted internal networks and enforce strict access controls to reduce attack surface. Maintain up-to-date backups and logs to facilitate incident response if incorrect permissions are detected.