Childhood maltreatment (CM), defined as caregiver-perpetrated abuse or neglect during childhood or adolescence, is associated with enduring social dysfunction. Adults with a history of CM often maintain greater interpersonal distance from both friends and strangers, regardless of relational closeness. Predictive-processing models suggest that such impairments may stem from the development of overly precise negative beliefs about others, which are resistant to updating, even in the face of contradictory information. The current study investigated whether the ability to form and update social beliefs varies as a function of CM history, and whether belief updating moderates the association between CM and posttraumatic stress disorder (PTSD) symptoms following trauma exposure in adulthood. One hundred and eighteen participants completed a battery of questionnaires and a performance-based task assessing belief formation and updating about friends and strangers. Results indicated no CM-related differences in initial belief formation. However, as predicted, adults with a CM history showed impaired belief updating when interacting with strangers. Importantly, deficits in stranger-related belief updating moderated the relationship between CM severity and PTSD symptoms: those with poor updating showed a stronger association between CM and PTSD, while those with greater flexibility in belief updating reported low symptom levels regardless of maltreatment severity. These findings suggest that CM may disrupt adaptive belief updating in interpersonal contexts, contributing to later vulnerability to psychopathology. The results highlight the potential value of targeting social cognitive processes, particularly belief updating, in interventions aimed at improving social functioning and psychological resilience among individuals with a history of CM.