Vulnerabilities

ownCloud Server versions from 10.6.0 up to (but not including) 10.13.1 accept WebDAV pre-signed URLs even when no signing key is configured for the file owner, an improper authentication flaw (CWE-287). A remote attacker who knows a victim's username can therefore access, modify, or delete that user's files without any credentials, with no privileges or user interaction required (CVSS 9.8). Any organization running a self-hosted ownCloud Server instance in the affected version range is exposed, especially internet-facing deployments. CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2026-08-27, confirming exploitation in the wild, and EPSS assigns a 43.2% probability of exploitation within 30 days (99th percentile). No public proof-of-concept code is known, but recent press reports of attacks against ownCloud (including theft of records at a Philippine research body) indicate active targeting of ownCloud flaws.

Do: Upgrade to ownCloud Server 10.13.1 or later immediately, prioritizing internet-facing instances, as the flaw is on CISA's KEV list with BOD 26-04 patching deadlines. Until patched, configure signing keys for users where possible and restrict internet exposure of the pre-signed URL/WebDAV endpoints, and review server logs for unauthenticated file access, modification, or deletion tied to known usernames. If mitigations are not available for a given deployment, follow BOD 26-04 guidance for cloud services or discontinue use of the product.