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Vulnerability record · CVE-2021-22915 · published 11 June 2021

CVE-2021-22915: Nextcloud server improper restriction of authentication attempts vulnerability

Nextcloud · Nextcloud Server

Nextcloud server before 19.0.11, 20.0.10, 21.0.2 is vulnerable to brute force attacks due to lack of inclusion of IPv6 subnets in rate-limiting considerations. This could potentially result in an attacker bypassing rate-limit controls such as the Nextcloud brute-force protection.

9.8 CVSS 3.1 Critical EPSS 1.7% · top 23.2% CWE-307 · Improper restriction of authentication attempts
9.8CVSS 3.1 base score, v2 5.0
1.7%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
8References
17 Jun 2026Last modified by NVD

Description

Nextcloud server before 19.0.11, 20.0.10, 21.0.2 is vulnerable to brute force attacks due to lack of inclusion of IPv6 subnets in rate-limiting considerations. This could potentially result in an attacker bypassing rate-limit controls such as the Nextcloud brute-force protection.

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

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://hackerone.com/reports/1154003 Permissions RequiredThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AGXGR6HYGQ6MZXISMJEHCOX
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L6BO6P6MP2MOWA6PZRXX32P
https://nextcloud.com/security/advisory/?id=NC-SA-2021-009 Broken Link
https://hackerone.com/reports/1154003 Permissions RequiredThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AGXGR6HYGQ6MZXISMJEHCOX
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L6BO6P6MP2MOWA6PZRXX32P
https://nextcloud.com/security/advisory/?id=NC-SA-2021-009 Broken Link

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Source: NIST National Vulnerability Database (record CVE-2021-22915), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.