Vulnerability-Lookup

GHSA-VV8X-44WW-J3WH

Vulnerability from github – Published: 2026-09-08 15:31 – Updated: 2026-09-09 03:30

Details

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.

Severity

6.5 (Medium)


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

7.1 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-73321"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-674"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-08T14:17:26Z",
    "severity": "HIGH"
  },
  "details": "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\u0027s stack limit, causing fatal errors that repeatedly terminate PHP-FPM workers for all visitors rendering the affected thread.",
  "id": "GHSA-vv8x-44ww-j3wh",
  "modified": "2026-09-09T03:30:36Z",
  "published": "2026-09-08T15:31:55Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-73321"
    },
    {
      "type": "WEB",
      "url": "https://bombobombone.github.io/posts/cve-2026-73321"
    },
    {
      "type": "WEB",
      "url": "https://github.com/BomboBombone/CVE-2026-73321"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser"
    },
    {
      "type": "WEB",
      "url": "https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856"
    },
    {
      "type": "WEB",
      "url": "https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-73321 (GCVE-0-2026-73321)

Vulnerability from cvelistv5 – Published: 2026-09-08 13:20 – Updated: 2026-10-01 15:20

Title

XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser

Summary

Severity

7.1 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

6.5 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-10 13:49 UTC

CWE

CWE-674 - Uncontrolled Recursion

Assigner

VulnCheck CNA under the mitre root

CNA scorecard B 84/100 over 6925 records in the last 180 days details

References

5 references

URL	Tags
https://xenforo.com/community/threads/security-fi…	vendor-advisorypatch
https://xenforo.com/community/threads/xenforo-2-3…	release-notes
https://bombobombone.github.io/posts/cve-2026-73321/	technical-description
https://github.com/BomboBombone/CVE-2026-73321	exploit
https://www.vulncheck.com/advisories/xenforo-unco…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
XenForo	XenForo	Affected: 0 , < 2.3.13 (semver) cpe:2.3:a:xenforo:xenforo::::::::

Date Public

2026-09-07 00:00

Credits

Marco Paciaroni (BomboBombone) VulnCheck

Show details on NVD website

JSON

To clipboard

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        "metrics": [
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                "id": "CVE-2026-73321",
                "options": [
                  {
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                  },
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                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-10T13:49:59.215010Z",
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    "cna": {
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    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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