What’s Vulnerable › Vulnerabilities

CVE-2021-22915

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-11 · updated 2026-06-17
• Weakness: CWE-307

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.

Affected products

• Fedoraproject Fedora: 33, 34
• Nextcloud Server: before 19.0.11; from 20.0.0 before 20.0.10; from 21.0.0 before 21.0.2 — fixed in 19.0.11, 20.0.10, 21.0.2

How to fix

Upgrade to a fixed version: Nextcloud Server 19.0.11, 20.0.10, 21.0.2. Check the vendor advisory for mitigations.

References

• https://hackerone.com/reports/1154003
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AGXGR6HYGQ6MZXISMJEHCOXRGRFRUFMA/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L6BO6P6MP2MOWA6PZRXX32PLWPXN5O4S/
• https://nextcloud.com/security/advisory/?id=NC-SA-2021-009
• https://hackerone.com/reports/1154003
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AGXGR6HYGQ6MZXISMJEHCOXRGRFRUFMA/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L6BO6P6MP2MOWA6PZRXX32PLWPXN5O4S/
• https://nextcloud.com/security/advisory/?id=NC-SA-2021-009

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