The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server. Starting with version 3.0.0 and prior to version 3.6.5, a malicious server administrator can recover and modify the contents of end-to-end encrypted files. Users should upgrade the Nextcloud Desktop client to 3.6.5 to receive a patch. No known workarounds are available.
Weakness
Nonces should be used for the present occasion and only once.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Desktop | Nextcloud | 3.0.0 (including) | 3.6.5 (excluding) |
| Nextcloud-desktop | Ubuntu | focal | * |
| Nextcloud-desktop | Ubuntu | kinetic | * |
| Nextcloud-desktop | Ubuntu | trusty | * |
| Nextcloud-desktop | Ubuntu | upstream | * |
| Nextcloud-desktop | Ubuntu | xenial | * |
Potential Mitigations
References
- https://ethz.ch/content/dam/ethz/special-interest/infk/inst-infsec/appliedcrypto/education/theses/report_DanieleCoppola.pdf
- https://github.com/nextcloud/desktop/pull/5324
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-4p33-rw27-j5fc
- https://ethz.ch/content/dam/ethz/special-interest/infk/inst-infsec/appliedcrypto/education/theses/report_DanieleCoppola.pdf
- https://github.com/nextcloud/desktop/pull/5324
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-4p33-rw27-j5fc
- https://lists.debian.org/debian-lts-announce/2025/09/msg00018.html