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: 2026-09-10 15:02

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 mitre root

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)

Date Public

2026-09-07 00:00

Credits

Marco Paciaroni (BomboBombone) VulnCheck

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-73321",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-10T13:49:59.215010Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-10T15:02:59.382Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "XenForo",
          "vendor": "XenForo",
          "versions": [
            {
              "lessThan": "2.3.13",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Marco Paciaroni (BomboBombone)"
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "VulnCheck"
        }
      ],
      "datePublic": "2026-09-07T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 7.1,
            "baseSeverity": "HIGH",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "LOW",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        },
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
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      "problemTypes": [
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          "descriptions": [
            {
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              "description": "Uncontrolled Recursion",
              "lang": "en",
              "type": "CWE"
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      "providerMetadata": {
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        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
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      },
      "references": [
        {
          "name": "Vendor Advisory",
          "tags": [
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            "patch"
          ],
          "url": "https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/"
        },
        {
          "name": "Release Notes",
          "tags": [
            "release-notes"
          ],
          "url": "https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/"
        },
        {
          "name": "Researcher Advisory",
          "tags": [
            "technical-description"
          ],
          "url": "https://bombobombone.github.io/posts/cve-2026-73321/"
        },
        {
          "name": "Researcher PoC",
          "tags": [
            "exploit"
          ],
          "url": "https://github.com/BomboBombone/CVE-2026-73321"
        },
        {
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser"
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "XenForo \u003c 2.3.13 Uncontrolled Recursion DoS via BBCode Parser",
      "x_generator": {
        "engine": "vulncheck"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-73321",
    "datePublished": "2026-09-08T13:20:16.081Z",
    "dateReserved": "2026-08-11T19:56:20.008Z",
    "dateUpdated": "2026-09-10T15:02:59.382Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

GHSA-VV8X-44WW-J3WH

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

Tags

Sightings

Nomenclature