RESTEasy CorsFilter Misconfiguration Enables Credential Theft

RESTEasy's CorsFilter contains a critical flaw in its cross-origin resource sharing (CORS) implementation that occurs when configured to allow all origins using the wildcard "*" pattern. The vulnerability reflects the requesting Origin header directly into the Access-Control-Allow-Origin response while simultaneously setting Access-Control-Allow-Credentials to true—a dangerous combination that violates CORS security principles. This misconfiguration allows attackers on malicious websites to make credentialed cross-origin requests against vulnerable applications and read authenticated responses from victim sessions. Any organization running RESTEasy with permissive CORS policies is at risk, particularly those handling sensitive user data or financial transactions where session hijacking could lead to unauthorized access and data exfiltration.

While this CVE doesn't map to specific MITRE ATT&CK techniques currently, Casky's 754 security skills—powered by Claude AI's extended reasoning—would detect the underlying attack patterns associated with cross-origin exploitation and credential compromise. Practitioners using Casky would identify suspicious CORS policy configurations through skills mapping to credential access and lateral movement patterns, seeing findings that highlight the dangerous combination of wildcard origin allowances paired with credential flags. The platform would flag requests originating from unexpected domains attempting to access authenticated endpoints, revealing the exploitation chain before attackers can exfiltrate sensitive data. By correlating configuration analysis with request pattern detection, Casky helps teams spot this vulnerability in their REST API implementations and remediate misconfigured CORS policies before active exploitation occurs.