Nextcloud Calendar up to 4.7.16/5.2.3 Attachment unexpected data type

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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4.5$0-$5k0.00

Summaryinfo

A vulnerability labeled as problematic has been found in Nextcloud Calendar up to 4.7.16/5.2.3. Impacted is an unknown function of the component Attachment Handler. Such manipulation leads to improper handling of unexpected data type. This vulnerability is documented as CVE-2025-66550. The attack can be executed remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Nextcloud Calendar up to 4.7.16/5.2.3 and classified as problematic. Affected by this issue is an unknown part of the component Attachment Handler. The manipulation with an unknown input leads to a improper handling of unexpected data type vulnerability. Using CWE to declare the problem leads to CWE-241. The product does not handle or incorrectly handles when a particular element is not the expected type, e.g. it expects a digit (0-9) but is provided with a letter (A-Z). Impacted is integrity. CVE summarizes:

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.

The advisory is available at github.com. This vulnerability is handled as CVE-2025-66550 since 12/04/2025. The exploitation is known to be easy. The attack may be launched remotely. Successful exploitation requires user interaction by the victim. The technical details are unknown and an exploit is not available.

Upgrading to version 4.7.17 or 5.2.4 eliminates this vulnerability.

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Productinfo

Type

Vendor

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.6
VulDB Meta Temp Score: 4.5

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 5.7
CNA Vector (GitHub_M): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Improper handling of unexpected data type
CWE: CWE-241 / CWE-229 / CWE-20
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Calendar 4.7.17/5.2.4

Timelineinfo

12/04/2025 CVE reserved
12/05/2025 +1 days Advisory disclosed
12/05/2025 +0 days VulDB entry created
12/05/2025 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2025-66550 (🔒)
GCVE (CVE): GCVE-0-2025-66550
GCVE (VulDB): GCVE-100-334526

Entryinfo

Created: 12/05/2025 18:18
Changes: 12/05/2025 18:18 (64)
Complete: 🔍
Cache ID: 216::103

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