Vulnerability in Nextcloud server

[ Description ]Official description

Abusing the federated share endpoint, an attacker can write arbitrary rows into the oc_share_external database table. These rows persist indefinitely — there is no automatic cleanup mechanism. Three distinct denial-of-service conditions follow from this write primitive, all triggered from the same unauthenticated source and all self-renewing on a 24-hour cycle for as long as the injected rows remain in the database.

[ Fixes ]Fixes and patches

• Security bulletin: Nextcloud GHSA-p9qq-6vpv-x7wjVendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-p9qq, cited by CERT-FR CERTFR-2026-AVI-1392
• Security bulletin: Nextcloud GHSA-w7pp-8m7c-555cVendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-w7pp, cited by CERT-FR CERTFR-2026-AVI-1392
• Security bulletin: Nextcloud GHSA-5572-968j-v7g5Vendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-5572, cited by CERT-FR CERTFR-2026-AVI-1392
• Security bulletin: Nextcloud GHSA-qwm4-h3xh-gmvcVendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-qwm4, cited by CERT-FR CERTFR-2026-AVI-1392
• Security bulletin: Nextcloud GHSA-x4hv-m8g6-5cj4Vendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-x4hv, cited by CERT-FR CERTFR-2026-AVI-1392
• Security bulletin: Nextcloud GHSA-6m4h-j3wr-v388Vendor patch or bulletin · CERT-FR · github.com/nextcloud/security-advisories/security/advisories/GHSA-6m4h, cited by CERT-FR CERTFR-2026-AVI-1392

[ Advisories ]Government CERT advisories

• CERT-FR27 Oct 2026CERTFR-2026-AVI-1392

  Multiple vulnerabilities in Nextcloud products Translated from French

  Multiple vulnerabilities have been discovered in Nextcloud products. Some of them allow an attacker to cause remote denial of service, a breach of data confidentiality and a security policy bypass.

  CVE-2026-67400CVE-2026-77173CVE-2026-77167+3 more CVEs
• BSI CERT-Bund26 Oct 2026WID-SEC-2026-4185

  Nextcloud (Server, Tables, Whiteboard, Files Confidential, Collectives, Richdocuments): Multiple vulnerabilities Translated from German

  CVE-2026-77171CVE-2026-82986CVE-2026-77167+7 more CVEs

[ References ]References

• hackerone.com/reports/3679640