The virtual filesystem in ownCloud Server before 6.0.9, 7.0.x before 7.0.7, and 8.0.x before 8.0.5 does not consider that NULL is a valid getPath return value, which allows remote authenticated users to bypass intended access restrictions and gain access to users files via a sharing link to a file with a deleted parent folder.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-5954
• https://owncloud.org/security/advisory/?id=oc-sa-2015-011
• http://www.debian.org/security/2015/dsa-3373