CVE-2021-32653Network attack vector

User ID disclosure via unconditional lookup synchronization

Published Jun 1, 2021 · Updated Aug 3, 2024

Information disclosure in Nextcloud Server before 19.0.11, 20.0.10, or 21.0.2 exposes user IDs to the lookup server. The lookup synchronization path submits every account identifier even when that account has no profile fields marked as published. The transfer occurs under default settings, disclosing identifiers to the configured remote lookup service without requiring an affected user to publish profile data.

CVSS severity2.7
Low
EPSS probability1.21%
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 before 19.0.11, 20.0.10, or 21.0.2 exposes user IDs to the lookup server. The lookup synchronization path submits every account identifier even when that account has no profile fields marked as published. The transfer occurs under default settings, disclosing identifiers to the configured remote lookup service without requiring an affected user to publish profile data.

The record

CVE
CVE-2021-32653
Published
Jun 1, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Security Advisories
Classifications
CWE-201
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Jun 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=< 19.0.11
  2. Affected versionversion=>= 20.0.0, < 20.0.10
  3. Affected versionversion=>= 21.0.0, < 21.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Nextcloud GmbH · Nextcloud Security Advisoriesversion=< 19.0.11; version=>= 20.0.0, < 20.0.10; version=>= 21.0.0, < 21.0.2

Published CVSS scores

2.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/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.

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

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-201Insertion of Sensitive Information Into Sent Data

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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