[Bug]: Unsupported VALUE parameter for DTEND property. You supplied "DATETIME"

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

The calendar file below causes sync to fail from Apple Calendar to Nextcloud.
I have abridged it from an .ics file downloaded from Avanti West Coast, a train company in the UK.

BEGIN:VCALENDAR
CALSCALE:GREGORIAN
METHOD:PUBLISH
PRODID:-//Booking Cal//EN
VERSION:2.0
BEGIN:VEVENT
DTSTAMP;VALUE=DATETIME:20260716T130000
UID:9361BC90-715B-4215-A31B-5CDB5E37B131
DTSTART;VALUE=DATETIME:20260716T130000
DTEND;VALUE=DATETIME:20260716T133000
END:VEVENT
END:VCALENDAR

Steps to reproduce

1. Import given file to Apple Calendar
2. Observe HTTP 500 on the client

Expected behavior

File should sync properly as it is valid according to https://icalendar.org/validator.html

Nextcloud Server version

33

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Apache (supported)

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

Upgraded to a MAJOR version (ex. 31 to 32)

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "a",
            "b",
            "c",
            "nextcloud-push-gateway",
            "d"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "https:\/\/a",
        "htaccess.RewriteBase": "\/",
        "dbtype": "mysql",
        "version": "33.0.5.1",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "mail_smtpmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "filelocking.enabled": true,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 0
        },
        "loglevel": 0,
        "mail_smtpsecure": "ssl",
        "maintenance": false,
        "theme": "",
        "mysql.utf8mb4": true,
        "updater.release.channel": "stable",
        "enable_previews": true,
        "enabledPreviewProviders": [
            "OC\\Preview\\Imaginary",
            "OC\\Preview\\MarkDown",
            "OC\\Preview\\MP3",
            "OC\\Preview\\TXT",
            "OC\\Preview\\Krita",
            "OCA\\Richdocuments\\Preview\\OpenDocument",
            "OC\\Preview\\Movie",
            "OC\\Preview\\Font",
            "OCA\\Richdocuments\\Preview\\MSExcel",
            "OCA\\Richdocuments\\Preview\\MSWord",
            "OCA\\Richdocuments\\Preview\\OOXML",
            "OC\\Preview\\MSOffice2007",
            "OCA\\Richdocuments\\Preview\\EMF",
            "OC\\Preview\\ImaginaryPDF",
            "OCA\\Richdocuments\\Preview\\Pdf"
        ],
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "465",
        "mail_smtpauth": 1,
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "data-fingerprint": "492f75b5a90a929e7bff3609193fb862",
        "app_install_overwrite": [
            "news"
        ],
        "default_phone_region": "DE",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "preview_imaginary_url": "***REMOVED SENSITIVE VALUE***",
        "defaultapp": "files,dashboard",
        "maintenance_window_start": 2,
        "allow_local_remote_servers": true,
        "bulkupload.enabled": false,
        "forbidden_filename_basenames": [
            "con",
            "prn",
            "aux",
            "nul",
            "com0",
            "com1",
            "com2",
            "com3",
            "com4",
            "com5",
            "com6",
            "com7",
            "com8",
            "com9",
            "com\u00b9",
            "com\u00b2",
            "com\u00b3",
            "lpt0",
            "lpt1",
            "lpt2",
            "lpt3",
            "lpt4",
            "lpt5",
            "lpt6",
            "lpt7",
            "lpt8",
            "lpt9",
            "lpt\u00b9",
            "lpt\u00b2",
            "lpt\u00b3"
        ],
        "forbidden_filename_characters": [
            "<",
            ">",
            ":",
            "\"",
            "|",
            "?",
            "*",
            "\\",
            "\/"
        ],
        "forbidden_filename_extensions": [
            " ",
            ".",
            ".filepart",
            ".part"
        ],
        "twofactor_enforced": "true",
        "twofactor_enforced_groups": [
            "admin"
        ],
        "twofactor_enforced_excluded_groups": [],
        "serverid": 0
    }
}

List of activated Apps

Enabled:
  - activity: 6.0.0
  - admin_audit: 1.23.0
  - bookmarks: 16.2.1
  - bruteforcesettings: 6.0.0
  - calendar: 6.4.2
  - circles: 33.0.0
  - cloud_federation_api: 1.17.0
  - comments: 1.23.0
  - contacts: 8.7.0
  - contactsinteraction: 1.14.1
  - cospend: 4.0.0
  - dashboard: 7.13.0
  - dav: 1.36.0
  - event_update_notification: 2.9.0
  - external: 8.0.1
  - federatedfilesharing: 1.23.0
  - federation: 1.23.0
  - files: 2.5.0
  - files_automatedtagging: 4.0.0
  - files_downloadlimit: 5.1.0
  - files_external: 1.25.1
  - files_linkeditor: 1.1.24
  - files_pdfviewer: 6.0.0
  - files_reminders: 1.6.0
  - files_sharing: 1.25.2
  - files_trashbin: 1.23.0
  - files_versions: 1.26.0
  - firstrunwizard: 6.0.0
  - groupfolders: 21.0.7
  - integration_paperless: 1.0.13
  - logreader: 6.0.0
  - lookup_server_connector: 1.21.0
  - news: 28.6.0
  - nextcloud_announcements: 5.0.0
  - notes: 6.0.0
  - notifications: 6.0.0
  - notify_push: 1.3.3
  - oauth2: 1.21.0
  - password_policy: 5.0.0
  - phonetrack: 1.2.0
  - photos: 6.0.0
  - privacy: 5.0.0
  - profile: 1.2.0
  - provisioning_api: 1.23.0
  - qownnotesapi: 26.5.0
  - recommendations: 6.0.0
  - related_resources: 4.0.0
  - richdocuments: 10.2.0
  - serverinfo: 5.0.0
  - settings: 1.16.0
  - sharebymail: 1.23.0
  - support: 5.0.0
  - survey_client: 5.0.0
  - systemtags: 1.23.0
  - tasks: 0.17.1
  - text: 7.0.1
  - theming: 2.8.0
  - twofactor_backupcodes: 1.22.0
  - twofactor_totp: 15.0.0
  - twofactor_webauthn: 2.7.0
  - updatenotification: 1.23.0
  - uppush: 2.5.0
  - user_oidc: 8.10.1
  - user_status: 1.13.0
  - viewer: 6.0.0
  - weather_status: 1.13.0
  - webhook_listeners: 1.5.0
  - workflowengine: 2.15.0
Disabled:
  - announcementcenter: 7.4.1 (installed 7.4.1)
  - app_api: 33.0.0 (installed 4.0.0)
  - apporder: 0.15.0 (installed 0.15.0)
  - camerarawpreviews: 1.1.1 (installed 1.1.1)
  - checksum: 2.1.2 (installed 2.1.2)
  - data_request: 5.0.0 (installed 5.0.0)
  - dav_push: 1.0.1 (installed 1.0.1)
  - dropit: 0.4.0 (installed 0.4.0)
  - encryption: 2.21.0
  - extract: 1.3.6 (installed 1.3.6)
  - files_downloadactivity: 1.18.1 (installed 1.18.1)
  - files_fulltextsearch: 33.0.0 (installed 33.0.0)
  - files_markdown: 2.4.1 (installed 2.4.1)
  - files_readmemd: 3.0.2 (installed 3.0.2)
  - files_rightclick: 0.15.1 (installed 1.6.0)
  - files_texteditor: 2.15.1 (installed 2.15.1)
  - fileslibreofficeedit: 2.0.1 (installed 2.0.1)
  - fulltextsearch: 33.0.0 (installed 33.0.0)
  - maps: 1.7.1 (installed 1.7.1)
  - metadata: 0.23.0 (installed 0.23.0)
  - polls: 9.1.4 (installed 9.1.4)
  - ransomware_protection: 1.14.0 (installed 1.14.0)
  - side_menu: 5.3.0 (installed 5.3.0)
  - socialsharing_email: 4.1.0 (installed 4.1.0)
  - spreed: 23.0.6 (installed 23.0.6)
  - suspicious_login: 11.0.0
  - tables: 2.2.0 (installed 2.2.0)
  - telephoneprovider: 1.0.3 (installed 1.0.3)
  - testing: 1.23.0
  - twofactor_admin: 4.11.1 (installed 4.11.1)
  - twofactor_nextcloud_notification: 7.0.0 (installed 3.10.0)
  - user_ldap: 1.24.0
  - workflow_script: 4.0.0 (installed 4.0.0)

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

{"reqId":"SHlWF1V4oQCLrCgd4TSE","level":3,"time":"2026-06-13T16:13:35+00:00","remoteAddr":"2a00:1e::","user":"x","app":"no app in context","method":"PUT","url":"/remote.php/dav/calendars/x/personal/9361BC90-715B-4215-A31B-5CDB5E37B131.ics","scriptName":"/remote.php","message":"Uncaught exception","userAgent":"macOS/26.5.1 (25F80) dataaccessd/1.0","version":"33.0.5.1","exception":{"Exception":"Sabre\\VObject\\InvalidDataException","Message":"Unsupported VALUE parameter for DTEND property. You supplied \"DATETIME\"","Code":0,"Trace":[{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php","line":456,"function":"createProperty","class":"Sabre\\VObject\\Document","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php","line":233,"function":"readProperty","class":"Sabre\\VObject\\Parser\\MimeDir","type":"->"},{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php","line":219,"function":"parseLine","class":"Sabre\\VObject\\Parser\\MimeDir","type":"->"},{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php","line":184,"function":"parseLine","class":"Sabre\\VObject\\Parser\\MimeDir","type":"->"},{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php","line":96,"function":"parseDocument","class":"Sabre\\VObject\\Parser\\MimeDir","type":"->"},{"file":"/var/www/html/3rdparty/sabre/vobject/lib/Reader.php","line":47,"function":"parse","class":"Sabre\\VObject\\Parser\\MimeDir","type":"->"},{"file":"/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php","line":803,"function":"read","class":"Sabre\\VObject\\Reader","type":"::"},{"file":"/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php","line":760,"function":"validateICalendar","class":"Sabre\\CalDAV\\Plugin","type":"->"},{"file":"/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"beforeCreateFile","class":"Sabre\\CalDAV\\Plugin","type":"->"},{"file":"/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php","line":1094,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/html/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":504,"function":"createFile","class":"Sabre\\DAV\\Server","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPut","class":"Sabre\\DAV\\CorePlugin","type":"->"},{"file":"/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php","line":472,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/html/apps/dav/lib/Connector/Sabre/Server.php","line":212,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/html/apps/dav/lib/Server.php","line":428,"function":"start","class":"OCA\\DAV\\Connector\\Sabre\\Server","type":"->"},{"file":"/var/www/html/apps/dav/appinfo/v2/remote.php","line":25,"function":"exec","class":"OCA\\DAV\\Server","type":"->"},{"file":"/var/www/html/remote.php","line":151,"args":["/var/www/html/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/var/www/html/3rdparty/sabre/vobject/lib/Document.php","Line":214,"message":"Uncaught exception","exception":"{\"class\":\"Sabre\\VObject\\InvalidDataException\",\"message\":\"Unsupported VALUE parameter for DTEND property. You supplied \\\"DATETIME\\\"\",\"code\":0,\"file\":\"/var/www/html/3rdparty/sabre/vobject/lib/Document.php:214\",\"trace\":\"#0 /var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php(456): Sabre\\VObject\\Document->createProperty()\\n#1 /var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php(233): Sabre\\VObject\\Parser\\MimeDir->readProperty()\\n#2 /var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php(219): Sabre\\VObject\\Parser\\MimeDir->parseLine()\\n#3 /var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php(184): Sabre\\VObject\\Parser\\MimeDir->parseLine()\\n#4 /var/www/html/3rdparty/sabre/vobject/lib/Parser/MimeDir.php(96): Sabre\\VObject\\Parser\\MimeDir->parseDocument()\\n#5 /var/www/html/3rdparty/sabre/vobject/lib/Reader.php(47): Sabre\\VObject\\Parser\\MimeDir->parse()\\n#6 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php(803): Sabre\\VObject\\Reader::read()\\n#7 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php(760): Sabre\\CalDAV\\Plugin->validateICalendar()\\n#8 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\CalDAV\\Plugin->beforeCreateFile()\\n#9 /var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php(1094): Sabre\\DAV\\Server->emit()\\n#10 /var/www/html/3rdparty/sabre/dav/lib/DAV/CorePlugin.php(504): Sabre\\DAV\\Server->createFile()\\n#11 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\DAV\\CorePlugin->httpPut()\\n#12 /var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php(472): Sabre\\DAV\\Server->emit()\\n#13 /var/www/html/apps/dav/lib/Connector/Sabre/Server.php(212): Sabre\\DAV\\Server->invokeMethod()\\n#14 /var/www/html/apps/dav/lib/Server.php(428): OCA\\DAV\\Connector\\Sabre\\Server->start()\\n#15 /var/www/html/apps/dav/appinfo/v2/remote.php(25): OCA\\DAV\\Server->exec()\\n#16 /var/www/html/remote.php(151): require_once('...')\\n#17 {main}\"}","CustomMessage":"Uncaught exception"},"id":"6a2d83ad9da42"}

Additional info

Extra user backend: user_oidc
Client: macOS Calendar.app 26.5.1
Nextcloud 33.0.5

Start with the failing PUT path in apps/dav/lib/Connector/Sabre/Server.php and follow validation into sabre/dav/lib/CalDAV/Plugin.php and 3rdparty/sabre/vobject/lib/Parser/MimeDir.php. Reproduce with the abridged calendar file and inspect how DTEND handles VALUE=DATETIME. Done means the supplied calendar syncs without the InvalidDataException and regression coverage verifies the behavior.