CVE-2026-33635 (GCVE-0-2026-33635)

Vulnerability from cvelistv5 – Published: 2026-03-26 20:30 – Updated: 2026-03-30 11:33
VLAI
Title
iCalendar has ICS injection via unsanitized URI property values
Summary
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.
Severity
4.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
CWE
  • CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')
Assigner
References
Impacted products
Vendor Product Version
icalendar icalendar Affected: >= 2.0.0, < 2.12.2
Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-33635",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-03-30T11:33:37.244425Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-03-30T11:33:48.950Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "icalendar",
          "vendor": "icalendar",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.0.0, \u003c 2.12.2"
            }
          ]
        }
      ],
      "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 4.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-93",
              "description": "CWE-93: Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-26T20:30:43.696Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq"
        },
        {
          "name": "https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265"
        },
        {
          "name": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml"
        }
      ],
      "source": {
        "advisory": "GHSA-pv9c-9mfh-hvxq",
        "discovery": "UNKNOWN"
      },
      "title": "iCalendar has ICS injection via unsanitized URI property values"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-33635",
    "datePublished": "2026-03-26T20:30:43.696Z",
    "dateReserved": "2026-03-23T14:24:11.619Z",
    "dateUpdated": "2026-03-30T11:33:48.950Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-33635",
      "date": "2026-05-27",
      "epss": "0.00044",
      "percentile": "0.13579"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-33635\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-03-26T21:17:07.287\",\"lastModified\":\"2026-04-10T15:49:23.240\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"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 dise\u00f1ada para gestionar archivos iCalendar en el formato definido por el RFC-5545. Desde la versi\u00f3n 2.0.0 hasta la versi\u00f3n 2.12.2, la serializaci\u00f3n de archivos .ics no depura correctamente los valores de las propiedades URI, lo que permite la inyecci\u00f3n ICS a trav\u00e9s de entradas controladas por un atacante, a\u00f1adiendo 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 l\u00ednea ICS final mediante el serializador normal, por lo que una carga \u00fatil 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 trav\u00e9s 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 leg\u00edtimos, tales como asistentes a\u00f1adidos, URL modificadas, alarmas u otros campos del calendario. La versi\u00f3n 2.12.2 contiene un parche para este problema.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N\",\"baseScore\":4.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"REQUIRED\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":2.8,\"impactScore\":1.4},{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N\",\"baseScore\":4.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"REQUIRED\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":2.8,\"impactScore\":1.4}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-93\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:icalendar_project:icalendar:*:*:*:*:*:ruby:*:*\",\"versionStartIncluding\":\"2.0.0\",\"versionEndExcluding\":\"2.12.2\",\"matchCriteriaId\":\"3BBE7B6B-857A-41B0-A38E-7FA77FDB1497\"}]}]}],\"references\":[{\"url\":\"https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265\",\"source\":\"security-advisories@github.com\",\"tags\":[\"Patch\"]},{\"url\":\"https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq\",\"source\":\"security-advisories@github.com\",\"tags\":[\"Exploit\",\"Mitigation\",\"Vendor Advisory\"]},{\"url\":\"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml\",\"source\":\"security-advisories@github.com\",\"tags\":[\"Mitigation\",\"Vendor Advisory\"]}]}}",
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-33635\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-03-30T11:33:37.244425Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-03-30T11:33:45.440Z\"}}], \"cna\": {\"title\": \"iCalendar has ICS injection via unsanitized URI property values\", \"source\": {\"advisory\": \"GHSA-pv9c-9mfh-hvxq\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV3_1\": {\"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\"}}], \"affected\": [{\"vendor\": \"icalendar\", \"product\": \"icalendar\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003e= 2.0.0, \u003c 2.12.2\"}]}], \"references\": [{\"url\": \"https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq\", \"name\": \"https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265\", \"name\": \"https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml\", \"name\": \"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml\", \"tags\": [\"x_refsource_MISC\"]}], \"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.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-93\", \"description\": \"CWE-93: Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027)\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-03-26T20:30:43.696Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-33635\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-03-30T11:33:48.950Z\", \"dateReserved\": \"2026-03-23T14:24:11.619Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-03-26T20:30:43.696Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





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.


Detection rules are retrieved from Rulezet.