Vulnerability-Lookup

CVE-2026-107843 (GCVE-0-2026-107843)

Vulnerability from cvelistv5 – Published: 2026-10-09 19:21 – Updated: 2026-10-09 19:21

Title

Contao: The registration module re-sends activation mails on any unauthenticated POST, with no throttle and no captcha check

Summary

Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12.

Severity

5.3 (Medium)


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

CWE

CWE-204 - Observable Response Discrepancy
CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7642 records in the last 180 days details

References

4 references

URL	Tags
https://github.com/contao/contao/security/advisor…	x_refsource_CONFIRM
https://github.com/contao/contao/commit/2ea6117f9…	x_refsource_MISC
https://github.com/contao/contao/releases/tag/5.3.50	x_refsource_MISC
https://github.com/contao/contao/releases/tag/5.7.12	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
contao	contao	Affected: >= 4.1.0, < 5.3.50 Affected: >= 5.4.0-RC1, < 5.7.12	guessed

Show details on NVD website

JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "contao",
          "vendor": "contao",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 4.1.0, \u003c 5.3.50"
            },
            {
              "status": "affected",
              "version": "\u003e= 5.4.0-RC1, \u003c 5.7.12"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-204",
              "description": "CWE-204: Observable Response Discrepancy",
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              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770: Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-09T19:21:32.011Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6"
        },
        {
          "name": "https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b"
        },
        {
          "name": "https://github.com/contao/contao/releases/tag/5.3.50",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/contao/contao/releases/tag/5.3.50"
        },
        {
          "name": "https://github.com/contao/contao/releases/tag/5.7.12",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/contao/contao/releases/tag/5.7.12"
        }
      ],
      "source": {
        "advisory": "GHSA-mfxh-vp55-7gc6",
        "discovery": "UNKNOWN"
      },
      "title": "Contao: The registration module re-sends activation mails on any unauthenticated POST, with no throttle and no captcha check"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-107843",
    "datePublished": "2026-10-09T19:21:32.011Z",
    "dateReserved": "2026-10-08T22:34:49.291Z",
    "dateUpdated": "2026-10-09T19:21:32.011Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-107843",
      "date": "2026-10-10",
      "epss": "0.00255",
      "percentile": "0.15787"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "contao",
                "vendor": "contao",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003e= 4.1.0, \u003c 5.3.50"
                  },
                  {
                    "status": "affected",
                    "version": "\u003e= 5.4.0-RC1, \u003c 5.7.12"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12."
          }
        ],
        "id": "CVE-2026-107843",
        "lastModified": "2026-10-09T20:17:10.167",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 5.3,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "LOW",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 1.4,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-10-09T20:17:10.167",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/contao/contao/releases/tag/5.3.50"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/contao/contao/releases/tag/5.7.12"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Received",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-204"
              },
              {
                "lang": "en",
                "value": "CWE-770"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    }
  }
}

FKIE_CVE-2026-107843

Vulnerability from fkie_nvd - Published: 2026-10-09 20:17 - Updated: 2026-10-09 20:17

Severity

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b
	security-advisories@github.com	https://github.com/contao/contao/releases/tag/5.3.50
	security-advisories@github.com	https://github.com/contao/contao/releases/tag/5.7.12
	security-advisories@github.com	https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "contao",
          "vendor": "contao",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 4.1.0, \u003c 5.3.50"
            },
            {
              "status": "affected",
              "version": "\u003e= 5.4.0-RC1, \u003c 5.7.12"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12."
    }
  ],
  "id": "CVE-2026-107843",
  "lastModified": "2026-10-09T20:17:10.167",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 1.4,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-10-09T20:17:10.167",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/contao/contao/releases/tag/5.3.50"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/contao/contao/releases/tag/5.7.12"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-204"
        },
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-MFXH-VP55-7GC6

Vulnerability from github – Published: 2026-10-09 20:54 – Updated: 2026-10-09 20:54

Summary

Contao: The registration module re-sends activation mails

Details

ModuleRegistration::compile() reaches its follow-up registration branch on any POST to a page carrying the module. That branch checks neither FORM_SUBMIT nor the captcha result computed immediately above it, and resendActivationMail() leads to OptInToken::send(), which has no rate limit at all.

Impact

Anyone on the internet can make a Contao installation send unlimited mail to an address of their choosing, from the site's own sender and reputation, at one outbound message per HTTP request. That is both a nuisance for the recipient and a deliverability risk for the site operator. The same request is a reliable account oracle for "this address has a pending registration on this site", which is exactly the sort of membership fact a public site is usually expected not to disclose.

Honest bound. The target must have an unconfirmed registration, that is tl_member.disable = 1 together with an unconfirmed reg- opt-in token. An attacker can create that state for an arbitrary address, since registration requires no ownership proof, but on a site where reg_activate is off the branch is unreachable.

Severity

5.3 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/core-bundle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.1.0"
            },
            {
              "fixed": "5.3.50"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/core-bundle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.4.0-RC1"
            },
            {
              "fixed": "5.7.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-107843"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-204",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-09T20:54:04Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "`ModuleRegistration::compile()` reaches its follow-up registration branch on **any** POST to a page carrying the module. That branch checks neither `FORM_SUBMIT` nor the captcha result computed immediately above it, and `resendActivationMail()` leads to `OptInToken::send()`, which has no rate limit at all.\n\n### Impact\n\nAnyone on the internet can make a Contao installation send unlimited mail to an address of their choosing, from the site\u0027s own sender and reputation, at one outbound message per HTTP request. That is both a nuisance for the recipient and a deliverability risk for the site operator. The same request is a reliable account oracle for \"this address has a pending registration on this site\", which is exactly the sort of membership fact a public site is usually expected not to disclose.\n\n**Honest bound.** The target must have an unconfirmed registration, that is `tl_member.disable = 1` together with an unconfirmed `reg-` opt-in token. An attacker can create that state for an arbitrary address, since registration requires no ownership proof, but on a site where `reg_activate` is off the branch is unreachable.",
  "id": "GHSA-mfxh-vp55-7gc6",
  "modified": "2026-10-09T20:54:04Z",
  "published": "2026-10-09T20:54:04Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/contao/contao"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contao/contao/releases/tag/5.3.50"
    },
    {
      "type": "WEB",
      "url": "https://github.com/contao/contao/releases/tag/5.7.12"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Contao: The registration module re-sends activation mails"
}

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.

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.

Action not permitted

CVE-2026-107843 (GCVE-0-2026-107843)

FKIE_CVE-2026-107843

GHSA-MFXH-VP55-7GC6

Impact

Tags

Sightings

Nomenclature

Related by attack behaviour