Is CVE-2026-73321 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-73321?

CVE-2026-73321 has a CVSS v3 severity of MEDIUM (6.5).

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CVE-2026-73321

Description

XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deeply nested BBCode tags. Attackers can craft a single malicious post with sufficient nesting depth to exceed PHP's stack limit, causing fatal errors that repeatedly terminate PHP-FPM workers for all visitors rendering the affected thread.