CVE-2019-18839

CVE-2019-18839 is a critical stored cross-site scripting (XSS) vulnerability affecting FUDForum 3.0.9 via the nlogin parameter, potentially leading to remote code execution. An authenticated attacker can exploit this by crafting a malicious POST request, which executes when an administrator views user information, allowing PHP file writes and arbitrary code execution on the server. With a CVSS score of 9.0 (CRITICAL), this vulnerability has a high impact on confidentiality, integrity, and availability, requiring user interaction but with low attack complexity. There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.