CVE-2025-66548

File-extension spoofing via unsanitized RTLO filenames

Published Dec 5, 2025 · Updated Dec 8, 2025

File-extension spoofing in affected Nextcloud Deck releases allows local users to disguise attachment types with RTLO characters. AttachmentList.vue rendered attacker-controlled attachment names as one bidirectional text span, while Description.vue inserted attachment.data directly as link text without removing U+202E. Deck access is required to supply the crafted name, and a recipient can be tricked into downloading a file whose real extension differs from the displayed one.

CVSS severity5.5
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

File-extension spoofing in affected Nextcloud Deck releases allows local users to disguise attachment types with RTLO characters. AttachmentList.vue rendered attacker-controlled attachment names as one bidirectional text span, while Description.vue inserted attachment.data directly as link text without removing U+202E. Deck access is required to supply the crafted name, and a recipient can be tricked into downloading a file whose real extension differs from the displayed one.

The record

CVE
CVE-2025-66548
Published
Dec 5, 2025
Updated
Dec 8, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-116, T1036.002
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 8, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.12.7
  2. Affected versionversion=>= 1.14.0-beta.1, < 1.14.4
  3. Affected versionversion=>= 1.15.0-beta.1, < 1.15.1

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=< 1.12.7; version=>= 1.14.0-beta.1, < 1.14.4; version=>= 1.15.0-beta.1, < 1.15.1

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
3.3GitHub, Inc.CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output
T1036.002Right-to-Left Override

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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