SEOWriting plugin for WordPress through 1.12.5 contains a stored cross-site scripting vulnerability that allows authenticated contributors to inject malicious JavaScript by exploiting an overly permissive KSES allowlist that explicitly permits the onload event handler on iframe elements. Attackers can store crafted JavaScript payloads in post content that execute when the affected post is viewed or previewed by higher-privileged users, potentially leading to privilege escalation or account compromise.