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TI-2026-51446 Aliases CVE-2026-73321GHSA-vv8x-44ww-j3wh

XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser

Priority MEDIUM 64CWE-674Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-674.

Summary

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 it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00614 49th percentileScored 2026-11-07
Public exploit Yes 2 exploit referencesTagged by NVD and the CNA
Fix Fixed XenForo (XenForo): 2.3.13

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
XenForoXenForobefore 2.3.132.3.13Patch availableCNA
  • XenForo VendorXenForo Affected before 2.3.13 Fixed in 2.3.13 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:*before 2.3.13VulnerableXenForo
  • cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:* Versions before 2.3.13 Vulnerable ·XenForo

Remediation

  • Fix · CNA XenForo (XenForo) Fixed in 2.3.13

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Advisory ·

    XenForo — xenforo.com/community/threads/security-fixes-released-for-a…

    14 records Highest priority Priority HIGH 4 HIGH, 5 MEDIUM, 5 LOW

    Other records, highest priority first

    • TI-2026-51441 XenForo < 2.3.13 Payment Replay via PayPal REST Payment ProviderPriority HIGH 77
    • TI-2026-51439 XenForo < 2.3.13 Signature Verification Bypass via PayPal REST WebhookPriority HIGH 77
    • TI-2026-51436 XenForo < 2.3.13 OAuth2 Authorization Code ReusePriority HIGH 74
    Show all 14 records → Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-73321
  2. 2026-10-03 Alias added: GHSA-vv8x-44ww-j3wh

References

Exploit 2

Patch 1

Other 1

  • TI-2026-51441 XenForo < 2.3.13 Payment Replay via PayPal REST Payment Provider CVSS 4.0HIGH 8.7
  • TI-2026-51439 XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook CVSS 4.0HIGH 8.7
  • TI-2026-51436 XenForo < 2.3.13 OAuth2 Authorization Code Reuse CVSS 4.0CRITICAL 9.1
  • TI-2026-51434 XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint CVSS 4.0CRITICAL 9.1
  • TI-2024-25701 Xenforo before 2.2.16 allows code injection. CVSS 3.1HIGH 8.8
  • TI-2026-51444 XenForo < 2.3.13 XSS via Dynamic Redirect Handler CVSS 4.0MEDIUM 5.1
See all 27 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences