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CVE-2026-33635

Estado: AnalizadaMedia (4.3)—

iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\r` or `\n` characters.

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That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.

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).

Tecnologías afectadas (1)

Icalendar Project — Icalendar

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-33635",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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          "id": "CVE-2026-33635",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-03-30T11:33:37.244425Z"
        }
      }
    ],
    "cvssMetricV31": [
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        "type": "Secondary",
        "source": "security-advisories@github.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 4.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 2.8
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
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          "baseScore": 4.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
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        "exploitabilityScore": 2.8
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      "affectedData": [
        {
          "vendor": "icalendar",
          "product": "icalendar",
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            {
              "status": "affected",
              "version": ">= 2.0.0, < 2.12.2"
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  "published": "2026-03-26T21:17:07.287",
  "references": [
    {
      "url": "https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265",
      "tags": [
        "Patch"
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    {
      "url": "https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq",
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        "Vendor Advisory"
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      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml",
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  "vulnStatus": "Analyzed",
  "weaknesses": [
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      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-93"
        }
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue."
    },
    {
      "lang": "es",
      "value": "iCalendar es una biblioteca de Ruby diseñada para gestionar archivos iCalendar en el formato definido por el RFC-5545. Desde la versión 2.0.0 hasta la versión 2.12.2, la serialización de archivos .ics no depura correctamente los valores de las propiedades URI, lo que permite la inyección ICS a través de entradas controladas por un atacante, añadiendo entradas de calendario arbitrarias a la salida. `Icalendar::Values::Uri` recurre a la cadena de entrada sin procesar cuando `URI.parse` falla y posteriormente la serializa con `value.to_s` sin eliminar ni escapar los caracteres \\r o \\n. Ese valor se incrusta directamente en la línea ICS final mediante el serializador normal, por lo que una carga útil que contenga CRLF puede terminar la propiedad original y crear una nueva propiedad o componente ICS. (Parece que, debido a esto, se puede inyectar a través de url, source, image, organizer, attach, attendee, conference y tzurl). Las aplicaciones que generan archivos `.ics` a partir de metadatos parcialmente no fiables se ven afectadas. Como resultado, los clientes de calendario o importadores posteriores pueden procesar el contenido proporcionado por el atacante como si se tratara de datos de eventos legítimos, tales como asistentes añadidos, URL modificadas, alarmas u otros campos del calendario. La versión 2.12.2 contiene un parche para este problema."
    }
  ],
  "lastModified": "2026-06-17T10:37:49.343",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "versionEndExcluding": "2.12.2",
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            }
          ],
          "operator": "OR"
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  "sourceIdentifier": "security-advisories@github.com"
}