CVE•Published 2026-09-08•Modified 2026-09-11•0 articles on news•6 live references•NVD data

CVE-2026-73321Xenforo · Xenforo

Vulnerability data via NVD (ingested)

CVSS v3.1

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS percentile

Exploit Prediction Scoring System · top 69% of all CVEs

Weaknesses (CWE)

CWE-674Uncontrolled Recursion

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.

Timeline

Published 2026-09-08

Modified 2026-09-11

External references

NVD MITRE Exploit-DB GitHub PoC trickest/cve VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag0 hosts

vuln:CVE-2026-73321

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Xenforo Xenforo"

All exposed Xenforo Xenforo instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Xenforo"

HTTP body or banner mentions "Xenforo" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2026-73321