CVE-2019-15621 — Improper permissions preservation in Nextcloud Server 16

Improper permissions preservation in Nextcloud Server 16.0.1 causes sharees to be able to reshare with write permissions when sharing the mount point of a share they received, as a public link.

01What is this vulnerability?

Improper permissions preservation in Nextcloud Server 16.0.1 causes sharees to be able to reshare with write permissions when sharing the mount point of a share they received, as a public link.

02Affected products

Vendor	Product	Versions
n	a / Nextcloud Server	16.0.2

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2020-02-04T19:08:57.000Z
• Last modified: 2024-08-05T00:56:22.056Z

09References

• hackerone.com — https://hackerone.com/reports/619484
• nextcloud.com — https://nextcloud.com/security/advisory/?id=NC-SA-2020-012
• lists.opensuse.org — http://lists.opensuse.org/opensuse-security-announce/2020-02/msg00019.html
• lists.opensuse.org — http://lists.opensuse.org/opensuse-security-announce/2020-02/msg00022.html