CVE-2026-42553

{
  "id": "CVE-2026-42553",
  "sourceIdentifier": "[email protected]",
  "published": "2026-05-27T18:16:22.857",
  "lastModified": "2026-10-26T11:10:00.157",
  "vulnStatus": "Deferred",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Cinny is a Matrix client. Prior to 4.10.3, A remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim's client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack. This is caused by an incorrect fallback in EmojiBoard that uses untrusted pack.meta.avatar (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used. Also, the service worker attaching the user's Authorization bearer token to all outbound GET requests whose URL contains /_matrix/client/v1/media/download or /_matrix/client/v1/media/thumbnail without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim's Authorization header (access token). This vulnerability is fixed in 4.10.3."
    },
    {
      "lang": "es",
      "value": "Cinny es un cliente Matrix. Antes de la versión 4.10.3, un atacante remoto autenticado que comparte una sala con una víctima y tiene permisos para crear ’emotes’ de sala (por ejemplo, en un mensaje directo) puede hacer que el cliente de la víctima envíe su token de acceso de Matrix a un servidor controlado por el atacante. Esto ocurre cuando la víctima abre el selector de emojis o pegatinas para la sala que contiene un paquete de ’emotes’ malicioso. Esto es causado por un ’fallback’ incorrecto en EmojiBoard que utiliza ’pack.meta.avatar’ no confiable (controlado por el usuario) sin convertirlo/validarlo como una URL MXC, permitiendo que se utilicen URL HTTP(S) arbitrarias. Además, el ’service worker’ adjunta el token ’bearer’ de autorización del usuario a todas las solicitudes GET salientes cuya URL contiene /_matrix/client/v1/media/download o /_matrix/client/v1/media/thumbnail sin verificar que el host de la solicitud coincida con el origen del ’homeserver’ configurado. Una URL controlada por el atacante que contenga esos fragmentos de ruta y CORS permisivo recibirá el encabezado de autorización de la víctima (token de acceso). Esta vulnerabilidad se corrige en la versión 4.10.3."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "cinnyapp",
          "product": "cinny",
          "versions": [
            {
              "version": "< 4.10.3",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV40": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "4.0",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/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",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "NONE",
          "vulnAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "subAvailabilityImpact": "NONE",
          "exploitMaturity": "NOT_DEFINED",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "valueDensity": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED"
        }
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-05-27T18:01:29.293909Z",
          "id": "CVE-2026-42553",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/cinnyapp/cinny/releases/tag/v4.10.3",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453",
      "source": "[email protected]"
    }
  ]
}