CVE-2021-37631Network attack vector

Authenticated board disclosure via missing Circle membership check

Published Sep 7, 2021 · Updated Aug 4, 2024

Authorization bypass in Nextcloud Deck before 1.2.9, 1.3.0 through 1.4.3, and 1.5.0 allows remote authenticated users to read Circle-shared boards. The board-sharing authorization path accepts a matching Circle ACL without verifying that the requesting account has a valid membership level in that Circle. Any authenticated account on the same Nextcloud instance can therefore read boards shared to a Circle it has not joined, while integrity and availability remain unaffected.

CVSS severity6.5
Medium
EPSS probability1.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Nextcloud Deck before 1.2.9, 1.3.0 through 1.4.3, and 1.5.0 allows remote authenticated users to read Circle-shared boards. The board-sharing authorization path accepts a matching Circle ACL without verifying that the requesting account has a valid membership level in that Circle. Any authenticated account on the same Nextcloud instance can therefore read boards shared to a Circle it has not joined, while integrity and availability remain unaffected.

The record

CVE
CVE-2021-37631
Published
Sep 7, 2021
Updated
Aug 4, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Security Advisories
Classifications
CWE-639, T1213
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=< 1.2.9
  2. Affected versionversion=>= 1.3.0, < 1.4.4
  3. Affected versionversion=>= 1.5.0, < 1.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Security Advisoriesversion=< 1.2.9; version=>= 1.3.0, < 1.4.4; version=>= 1.5.0, < 1.5.1

Published CVSS scores

6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:P/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
T1213Data from Information Repositories

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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