VulnerabilityPublished 5 Dec 2025Updated 8 Dec 2025

CVE-2025-66549: nextcloud security-advisories · Generation of Error Message Containing Sensitive Information

Affects nextcloud security-advisoriesSource CVE Database V5

Not known to be exploited · CVSS 2.4 Low : upgrade to 3.16.5 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

2.4Low

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 22% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.16.5

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: High
User Interaction: Required
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 5 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade nextcloud/desktop to 3.16.5.

Affected software

Product	Affected	Fixed in
GitHubnextcloud/desktop`pkg:github/nextcloud/desktop`Other threats	Affected <3.16.5	Fixed in 3.16.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade all Nextcloud Desktop clients to version 3.16.5 or later to ensure the vulnerability is patched.
Review and restrict access to server log files to minimize the number of administrators or personnel who can view sensitive metadata.
Implement log management policies that avoid logging sensitive file path information or sanitize logs to redact such data.
Educate users about the risks of manual file locking within encrypted directories and encourage minimizing this action unless necessary.
Monitor server logs for any unusual access patterns or attempts to extract sensitive metadata.
Consider deploying network-level encryption or VPNs to add an additional layer of protection for communications between clients and servers.
Conduct regular security audits focusing on metadata leakage risks in encrypted environments.
Coordinate with Nextcloud support or community for any additional security advisories or best practices related to metadata protection.

Description

Nextcloud Desktop is the desktop sync client for Nextcloud. Prior to 3.16.5, when trying to manually lock a file inside an end-to-end encrypted directory, the path of the file was sent to the server unencrypted, making it possible for administrators to see it in log files. This vulnerability is fixed in 3.16.5.

Impact

For European organizations, the primary impact of CVE-2025-66549 is the potential exposure of sensitive file path metadata to server administrators. This can lead to indirect confidentiality breaches by revealing organizational structures, project details, or user activities. Although the file contents remain protected by end-to-end encryption, metadata leakage can aid targeted attacks or insider threats. Organizations with strict data privacy requirements, such as those governed by GDPR, may face compliance risks if sensitive information is inadvertently exposed. The vulnerability does not affect data integrity or availability, and exploitation requires administrator access to logs and user interaction, limiting the attack surface. However, in environments where multiple administrators exist or where logs are widely accessible, the risk of unauthorized information disclosure increases. The impact is more significant for sectors handling sensitive or regulated data, such as finance, healthcare, and government agencies. Prompt patching mitigates these risks effectively.

CWE-209Generation of Error Message Containing Sensitive Information (opens in a new tab)
Base weaknessLikelihood of exploit: HighOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product generates an error message that includes sensitive information about its environment, users, or associated data.
Implementation
Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended).
Implementation
Handle exceptions internally and do not display errors containing potentially sensitive information to a user.
Implementation · Attack Surface Reduction
Use naming conventions and strong types to make it easier to spot when sensitive data is being used. When creating structures, objects, or other complex entities, separate the sensitive and non-sensitive data as much as possible.
OWASP Cheat Sheets
Error Handling (opens in a new tab)
Logging (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.4 (opens in a new tab)
V14.3.3 (opens in a new tab)
V7.3.3 (opens in a new tab)
Attack patterns
Fuzzing for application mapping (opens in a new tab)
Padding Oracle Crypto Attack (opens in a new tab)
Query System for Information (opens in a new tab)
Blind SQL Injection (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Dec 2025, 19:08 UTC

WeaknessesCWE-209

Technical details

References

Community reviews

Related threats