FKIE_CVE-2026-27477

Vulnerability from fkie_nvd - Published: 2026-02-24 20:27 - Updated: 2026-02-26 21:17
Severity ?
5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Summary
Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, an unauthenticated attacker can register a FASP with an attacker-chosen `base_url` that includes or resolves to a local / internal address, leading to the Mastodon server making requests to that address. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can force the Mastodon server to make http(s) requests to internal systems. While they cannot control the full URL that is being requested (only the prefix) and cannot see the result of those requests, vulnerabilities or other undesired behavior could be triggered in those systems. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental "fasp" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected.
References
security-advisories@github.comhttps://github.com/mastodon/mastodon/commit/7b85d2182361e68d51d9a02f94fb1070b5f503b1Patch
security-advisories@github.comhttps://github.com/mastodon/mastodon/security/advisories/GHSA-46w6-g98f-wxqmVendor Advisory, Patch
Impacted products
Vendor Product Version
joinmastodon mastodon *
joinmastodon mastodon *
To clipboard 

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "F8A96B12-8C08-4A0C-88A8-B7B2B7AED3BF",
              "versionEndExcluding": "4.4.14",
              "versionStartIncluding": "4.4.0",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "65E9009A-6D3F-4758-8EAA-6D832F06F3F6",
              "versionEndExcluding": "4.5.7",
              "versionStartIncluding": "4.5.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, an unauthenticated attacker can register a FASP with an attacker-chosen `base_url` that includes or resolves to a local / internal address, leading to the Mastodon server making requests to that address. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can force the Mastodon server to make http(s) requests to internal systems. While they cannot control the full URL that is being requested (only the prefix) and cannot see the result of those requests, vulnerabilities or other undesired behavior could be triggered in those systems. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental \"fasp\" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected."
    },
    {
      "lang": "es",
      "value": "Mastodon es un servidor de red social gratuito, de c\u00f3digo abierto, basado en ActivityPub. El registro de FASP requiere aprobaci\u00f3n manual por parte de un administrador. En las versiones 4.4.0 a 4.4.13 y 4.5.0 a 4.5.6, un atacante no autenticado puede registrar un FASP con una \u0027base_url\u0027 elegida por el atacante que incluye o se resuelve en una direcci\u00f3n local / interna, lo que lleva al servidor de Mastodon a realizar solicitudes a esa direcci\u00f3n. Esto solo afecta a los servidores de Mastodon que han optado por probar la caracter\u00edstica experimental FASP estableciendo la variable de entorno \u0027EXPERIMENTAL_FEATURES\u0027 a un valor que incluya \u0027fasp\u0027. Un atacante puede forzar al servidor de Mastodon a realizar solicitudes http(s) a sistemas internos. Aunque no pueden controlar la URL completa que se solicita (solo el prefijo) y no pueden ver el resultado de esas solicitudes, se podr\u00edan activar vulnerabilidades u otros comportamientos no deseados en esos sistemas. La soluci\u00f3n est\u00e1 incluida en las versiones 4.4.14 y 4.5.7. Los administradores que est\u00e1n probando activamente la caracter\u00edstica experimental \u0027fasp\u0027 deber\u00edan actualizar sus sistemas. Los servidores que no utilizan la bandera de caracter\u00edstica experimental \u0027fasp\u0027 no se ven afectados."
    }
  ],
  "id": "CVE-2026-27477",
  "lastModified": "2026-02-26T21:17:15.260",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 4.6,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "UNREPORTED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/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",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-02-24T20:27:50.173",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/mastodon/mastodon/commit/7b85d2182361e68d51d9a02f94fb1070b5f503b1"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Vendor Advisory",
        "Patch"
      ],
      "url": "https://github.com/mastodon/mastodon/security/advisories/GHSA-46w6-g98f-wxqm"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-918"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}


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  • 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.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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