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Deck app allows to spoof file extensions by using RTLO characters

Low
nickvergessen published GHSA-xjvq-xvr7-xpg6 Dec 5, 2025

Package

Deck (Nextcloud)

Affected versions

< 1.12.7, < 1.14.4, < 1.15.1

Patched versions

1.12.7, 1.14.4, 1.15.1

Description

Impact

File extension can be spoofed by using RTLO characters, tricking users into download files with a different extension than what is displayed.

Patches

It is recommended that Nextcloud Deck is upgraded to 1.12.7, 1.14.4 or 1.15.1.

Workarounds

  • Disable the Deck app

References

For more information

If you have any questions or comments about this advisory:

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CVE ID

CVE-2025-66548

Weaknesses

Improper Encoding or Escaping of Output

The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved. Learn more on MITRE.