CVE-2026-35210: OpenCTI: Authorization Bypass via `synchronized-upsert` HTTP Header Injection

OpenCTI is an open source platform for managing cyber threat intelligence knowledge and observables. Prior to 7.260326.0, an authorization bypass vulnerability in OpenCTI allows any authenticated user with KNOWLEDGEKNUPDATE permission to bypass Confidence Level validation and Object Marking restrictions by injecting the synchronized-upsert: true HTTP header, enabling attackers to downgrade confidence levels, remove security markings such as TLP:RED, manipulate relationships, and affect STIX object types including Indicators, ThreatActors, Malware, and Reports. This issue is fixed in version 7.260326.0.