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SSRF protection bypass in calendar subscriptions (NC-SA-2020-014)

12th December 2019

Risk level: Low

CVSS v3 Base Score: 6.3 (AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L)

CWE: Server-Side Request Forgery (SSRF) (CWE-918)

HackerOne report: 736867


A missing check for IPv4 nested inside IPv6 in Nextcloud server 17.0.1 allowed a SSRF when subscribing to a malicious calendar URL.

Affected Software

  • Nextcloud Server < 17.0.2 (CVE-2020-8138)
  • Nextcloud Server < 16.0.7 (CVE-2020-8138)
  • Nextcloud Server < 15.0.14 (CVE-2020-8138)

Action Taken

The error has been fixed.


It is recommended that the Nextcloud server is upgraded to 17.0.2.


The Nextcloud team thanks the following people for their research and responsible disclosure of the above advisory:

This advisory is licensed CC BY-SA 4.0.

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