PatchTheCVECVE-2026-73321: XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authen
CVE-2026-73321 is a medium-severity flaw (CVSS 6.5) affecting xenforo. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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.
Why this priority
- Public exploit reference
A fixed release or distro patch exists.
Risk facts
| CVSS score | 6.5 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 0.6% (top 51%) |
| CISA exploited list | No |
| Weakness | CWE-674 |
| Published | 2026-09-08 |
| Last modified | 2026-09-11 |
Last updated 2026-09-11 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-73321?
xenforo: upgrade to 2.3.13. Exact commands for each OS are on this page.
Is CVE-2026-73321 being exploited?
CVE-2026-73321 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-73321 affect?
CVE-2026-73321 affects xenforo. Severity is medium (CVSS 6.5). 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
How urgent is CVE-2026-73321?
Priority 40/100. Public exploit reference
Software pages
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