Here are a few options, depending on where the title will be used, all maintaining a formal tone:
- COAS Declares Misinformation a National Security Threat
- Army Chief Identifies Misinformation as an Emerging Security Threat
- COAS Categorizes Misinformation as a Significant Security Challenge
Recommendation: The first option (COAS Declares Misinformation a National Security Threat) is the most standard and professional choice for a news headline.