CVE-2025-66510Network attack vector

Contact-data disclosure via ignored address-book setting

Published Dec 5, 2025 · Updated Dec 5, 2025

Information disclosure in Nextcloud Server and Enterprise Server allows remote authenticated users to read unrelated users' contact data. The /contactsmenu/contacts endpoint registers and returns the system address book even when dav.system_addressbook_exposed is set to no. An authenticated account and a crafted contacts search are required; exposure is limited to names, email addresses, and identifiers.

CVSS severity4.5
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Nextcloud Server and Enterprise Server allows remote authenticated users to read unrelated users' contact data. The /contactsmenu/contacts endpoint registers and returns the system address book even when dav.system_addressbook_exposed is set to no. An authenticated account and a crafted contacts search are required; exposure is limited to names, email addresses, and identifiers.

The record

CVE
CVE-2025-66510
Published
Dec 5, 2025
Updated
Dec 5, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-359, T1087
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 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=< 31.0.10
  2. Affected versionversion=>= 32.0.0beta1, < 32.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=< 31.0.10; version=>= 32.0.0beta1, < 32.0.1

Published CVSS scores

4.5GitHubCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:N/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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-359Exposure of Private Personal Information to an Unauthorized Actor
T1087Account Discovery

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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