Quick answers
- Is CVE-2026-73321 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-73321 being exploited in the wild.
- How severe is CVE-2026-73321?
- Medium severity, with a CVSS score of 6.5, published 8 September 2026.
- Which products and versions are affected?
- XenForo XenForo before 2.3.13.
- Is there a fix for CVE-2026-73321?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-73321 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-73321?
- Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An uncontrolled recursion vulnerability exists in XenForo's BBCode parser where the maximum-depth limit is enforced after recursive parsing has already consumed stack memory, not before. An unauthenticated attacker can submit a specially crafted BBCode payload with 5,000 nested [quote] tags (approximately 75 KB) to the publicly accessible editor/to-html endpoint, causing the PHP worker process to exceed the stack limit and terminate with a stack overflow exception. This denial of service is repeatable per request, and concurrent malicious requests can temporarily exhaust the available worker pool. The vulnerability was fixed in XenForo 2.3.13 by moving the depth-limit check before recursive parsing.
Affected products
- XenForo XenForo before 2.3.13
Timeline
- 2026-09-08: disclosed