CVE-2026-39971 (GCVE-0-2026-39971)

Vulnerability from cvelistv5 – Published: 2026-04-14 23:35 – Updated: 2026-04-15 16:22
VLAI
Title
Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST
Summary
Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.
Severity
7.2 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
SSVC
Exploitation: poc Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-15 16:20 UTC
CWE
  • CWE-113 - Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7838 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
s9y Serendipity Affected: < 2.6.0
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-39971",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-04-15T16:20:55.327550Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-04-15T16:22:04.004Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "Serendipity",
          "vendor": "s9y",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.6.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER[\u0027HTTP_HOST\u0027] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker\u0027s domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.2,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "CHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-113",
              "description": "CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers (\u0027HTTP Request/Response Splitting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-14T23:35:49.305Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"
        },
        {
          "name": "https://github.com/s9y/Serendipity/releases/tag/2.6.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/s9y/Serendipity/releases/tag/2.6.0"
        }
      ],
      "source": {
        "advisory": "GHSA-458g-q4fh-mj6r",
        "discovery": "UNKNOWN"
      },
      "title": "Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-39971",
    "datePublished": "2026-04-14T23:35:49.305Z",
    "dateReserved": "2026-04-08T00:01:47.627Z",
    "dateUpdated": "2026-04-15T16:22:04.004Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-39971",
      "date": "2026-10-27",
      "epss": "0.00255",
      "percentile": "0.16993"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "Serendipity",
                "vendor": "s9y",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 2.6.0"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:s9y:serendipity:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "25355E06-ECC8-4A6C-ADB1-1A8ED17E5ABF",
                    "versionEndExcluding": "2.6.0",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:a:s9y:serendipity:2.6.0:beta1:*:*:*:*:*:*",
                    "matchCriteriaId": "D31C5F34-5B83-4955-870B-0D1AC375DA24",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER[\u0027HTTP_HOST\u0027] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker\u0027s domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0."
          },
          {
            "lang": "es",
            "value": "Serendipity es un motor de weblog impulsado por PHP. En las versiones 2.6-beta2 e inferiores, la funcionalidad de env\u00edo de correo electr\u00f3nico en include/functions.inc.php inserta $_SERVER[\u2019HTTP_HOST\u2019] directamente en el encabezado SMTP Message-ID sin validaci\u00f3n, y la funci\u00f3n de saneamiento existente serendipity_isResponseClean() no se llama en HTTP_HOST antes de incrustarlo. Un atacante que puede controlar el encabezado Host durante una acci\u00f3n que desencadena un correo electr\u00f3nico, como notificaciones de comentarios o correos electr\u00f3nicos de suscripci\u00f3n, puede inyectar encabezados SMTP arbitrarios en los correos electr\u00f3nicos salientes. Esto permite la suplantaci\u00f3n de identidad, el secuestro de respuestas a trav\u00e9s de la manipulaci\u00f3n del encadenamiento de Message-ID, y el abuso de la reputaci\u00f3n del correo electr\u00f3nico a trav\u00e9s del dominio del atacante incrustado en los encabezados de correo leg\u00edtimos. Este problema ha sido solucionado en la versi\u00f3n 2.6.0."
          }
        ],
        "id": "CVE-2026-39971",
        "lastModified": "2026-10-26T22:10:00.163",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 7.2,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "LOW",
                "integrityImpact": "LOW",
                "privilegesRequired": "NONE",
                "scope": "CHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 2.7,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-39971",
                "options": [
                  {
                    "exploitation": "poc"
                  },
                  {
                    "automatable": "yes"
                  },
                  {
                    "technicalImpact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-04-15T16:20:55.327550Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-04-15T04:17:39.763",
        "references": [
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Patch"
            ],
            "url": "https://github.com/s9y/Serendipity/releases/tag/2.6.0"
          },
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Exploit",
              "Mitigation",
              "Vendor Advisory"
            ],
            "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-113"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "current_release_date": "2026-06-05T19:12:50+00:00",
      "cve": "CVE-2026-39971",
      "id": "CVE-2026-39971",
      "initial_release_date": "2026-01-01T00:00:00+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39971.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-39971",
                    "options": [
                      {
                        "Exploitation": "poc"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-04-15T16:20:55.327550Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-04-15T16:20:59.391Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "product": "Serendipity",
              "vendor": "s9y",
              "versions": [
                {
                  "status": "affected",
                  "version": "\u003c 2.6.0"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER[\u0027HTTP_HOST\u0027] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker\u0027s domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 7.2,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "LOW",
                "integrityImpact": "LOW",
                "privilegesRequired": "NONE",
                "scope": "CHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
                "version": "3.1"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-113",
                  "description": "CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers (\u0027HTTP Request/Response Splitting\u0027)",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-04-14T23:35:49.305Z",
            "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
            "shortName": "GitHub_M"
          },
          "references": [
            {
              "name": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r",
              "tags": [
                "x_refsource_CONFIRM"
              ],
              "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"
            },
            {
              "name": "https://github.com/s9y/Serendipity/releases/tag/2.6.0",
              "tags": [
                "x_refsource_MISC"
              ],
              "url": "https://github.com/s9y/Serendipity/releases/tag/2.6.0"
            }
          ],
          "source": {
            "advisory": "GHSA-458g-q4fh-mj6r",
            "discovery": "UNKNOWN"
          },
          "title": "Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "assignerShortName": "GitHub_M",
        "cveId": "CVE-2026-39971",
        "datePublished": "2026-04-14T23:35:49.305Z",
        "dateReserved": "2026-04-08T00:01:47.627Z",
        "dateUpdated": "2026-04-15T16:22:04.004Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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

Sightings and recorded dates, grouped by day · UTC

JSON

Loading timeline…




    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.