The accelerated proliferation of social networking platforms, particularly Instagram, alongside a fundamental transformation in traditional news consumption, has increasingly exposed public trust in media narratives to extensive cognitive, social, and contextual vulnerabilities. This challenge is especially salient within the Middle East's pluralistic and polarized media landscape, where fabricated news and source verification ambiguities continuously compound the problem. To this end, the present study investigated the cognitive factors and social triggers affecting trust in Instagram news, alongside the moderating role of cultural dimensions among Iranian and Iraqi users. This employed a cross-sectional survey design, with active Instagram users in both countries comprising the statistical population. Based on SEM sample size requirements, 384 participants (192 per nation) were selected via convenience sampling. Data were gathered using a standardized questionnaire from validated international scales, built around second-order constructs. Empirical data were analyzed via PLS-SEM using SmartPLS software. Direct hypothesis tests revealed that cognitive factors (media literacy, self-efficacy, self-regulation) significantly decreased trust in Instagram news (β = -0.154, t = 3.441, p = 0.001). Conversely, social triggers (in-group cues, social proof) showed a strong positive effect on trust formation (β = 0.313, t = 6.884, p = 0.000). However, the moderating influence of Hofstede's cultural dimensions was not statistically significant. Additionally, multigroup analysis (PLS-MGA) confirmed the stability and homogeneity of news processing mechanisms across users in both countries. Collectively, these results highlight the urgent necessity of revising critical media literacy programs and enhancing transparency in authenticating digital news sources.