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CVE-2026-91121

Estado: AplazadaMedia (5)—

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, attacker-controlled upload filenames used in chat message excerpts were rendered as unescaped HTML. A user able to upload a file and send chat content could place markup in a filename that was then interpreted by chat channel lists, chat summary emails, pinned message bars, reply previews, thread previews, and other excerpt renderers.

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The issue allowed trusted-HTML injection that altered rendered excerpt content, but JavaScript execution was not demonstrated with default Content Security Policy settings. The advisory states that no confidentiality, integrity, or availability impact was identified, while its structured scoring metadata separately assigns low integrity impact. Sites that disable or relax the default CSP have increased exposure. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vector AV:N/PR:L permite T1190 (app expuesta). CWE-79 (XSS) + inyección HTML no escapada en nombres de fichero = T1189 (reflected/stored XSS en excerpt renderers). Integridad baja confirmada; ejecución JS depende de CSP relajado.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Vulnerability ScanningRestrict File and Directory PermissionsPrivileged Account ManagementRemote Data StorageNetwork SegmentationLimit Access to Resource Over Network

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Discourse — DiscourseAI

CWE

Referencias

JSON original (NVD)

Mostrar
{
  "id": "CVE-2026-91121",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-91121",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-09-24T17:27:35.450393Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security-advisories@github.com",
        "cvssData": {
          "scope": "CHANGED",
          "version": "3.1",
          "baseScore": 5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 3.1
      }
    ]
  },
  "affected": [
    {
      "source": "security-advisories@github.com",
      "affectedData": [
        {
          "vendor": "discourse",
          "product": "discourse",
          "versions": [
            {
              "status": "affected",
              "version": "< 2026.8.0"
            },
            {
              "status": "affected",
              "version": ">= 2026.7.0-latest, < 2026.7.2"
            },
            {
              "status": "affected",
              "version": ">= 2026.6.0-latest, < 2026.6.3"
            },
            {
              "status": "affected",
              "version": ">= 2026.1.0-latest, < 2026.1.8"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-09-24T18:19:06.583",
  "references": [
    {
      "url": "https://github.com/discourse/discourse/commit/24cd7cc4c868f20e6037d67d801d60c3e289b278",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/6e7a181909c34a059d2b0a6291335a363205b787",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/9d6f5e64a1cb68e8208520e4209b361e14f7394b",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/af197941f7613a3845cba21d217641c77c8ef836",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/pull/42882",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/security/advisories/GHSA-34rh-wjfv-65gq",
      "source": "security-advisories@github.com"
    }
  ],
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, attacker-controlled upload filenames used in chat message excerpts were rendered as unescaped HTML. A user able to upload a file and send chat content could place markup in a filename that was then interpreted by chat channel lists, chat summary emails, pinned message bars, reply previews, thread previews, and other excerpt renderers. The issue allowed trusted-HTML injection that altered rendered excerpt content, but JavaScript execution was not demonstrated with default Content Security Policy settings. The advisory states that no confidentiality, integrity, or availability impact was identified, while its structured scoring metadata separately assigns low integrity impact. Sites that disable or relax the default CSP have increased exposure. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0."
    }
  ],
  "lastModified": "2026-09-24T18:19:06.720",
  "sourceIdentifier": "security-advisories@github.com"
}