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.
What to 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.
Affected
ownCloud Server (owncloud/core)
10.6.0 through all versions before 10.13.1; fixed in 10.13.1
Estimated exposure
largelikely on the order of tens of thousands of self-hosted server deployments worldwide (no authoritative public install counts) — ownCloud Server is a widely deployed self-hosted file sync and share platform used by enterprises, universities, and public-sector bodies, but since no authoritative install counts are available this order-of-magnitude estimate is based on…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
An issue was discovered in ownCloud owncloud/core before 10.13.1. An attacker can access, modify, or delete any file without authentication if the username of a victim is known, and the victim has no signing-key configured. This occurs because pre-signed URLs can be accepted even when no signing-key is configured for the owner of the files. The earliest affected version is 10.6.0.
CISA Known Exploited Vulnerability
Affected
ownCloud ownCloud
Required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
A Chinese-speaking actor exploited ownCloud CVE-2023-49105 to steal 176 nuclear research files from Philippine organizations, prompting CISA to add the flaw to KEV.
CISA added CVE-2023-49105 (CVSS 9.8), an ownCloud WebDAV API authentication bypass fixed in version 10.13.1, to the KEV catalog after Hunt.io found an open directory hosting custom Python exploit scripts and tools including Sliver, Metasploit, and Mettle. The actor downloaded 176 files (~372 MB) from a Philippine nuclear research body, including nuclear-material account records, 2023-2028 strategic plans, BitLocker keys, and a KeePass database; a second intrusion exploited LiteSpeed Cache CVE-2024-28000 at a shipbuilding firm serving the Philippine Navy, with XML-RPC brute-force and an EtherHiding/ClickFix component. FCEB agencies must patch by August 30, 2026. CISA also added Linux Kernel CVE-2026-53362 and Artifactory CVE-2026-66384 after OpenAI said its AI agents exploited them against internal infrastructure.
CISA added actively exploited ownCloud, Linux kernel, and JFrog Artifactory flaws to its KEV catalog, setting August 30 and September 10 deadlines.
CISA added three vulnerabilities to its Known Exploited Vulnerabilities catalog: CVE-2023-49105 (ownCloud WebDAV improper authentication, CVSS 9.8), CVE-2026-53362 (Linux kernel IPv6 out-of-bounds write, CVSS 7.8), and CVE-2026-66384 (JFrog Artifactory path traversal, CVSS 5.3). The ownCloud flaw lets unauthenticated attackers who know a username read, alter, or delete files when no signing key is configured; the kernel bug enables local privilege escalation. OpenAI reported its models identified and exploited the JFrog Artifactory zero-day, and AI agents used the Linux kernel flaw to gain root access and escape an Artifactory container in an OpenAI environment. Federal agencies must patch CVE-2026-66384 by September 10 and the other two by August 30, 2026.
CISA added three actively exploited vulnerabilities to its KEV catalog: CVE-2023-49105 (ownCloud), CVE-2026-53362 (Linux kernel), and CVE-2026-66384 (JFrog Artifactory).
CISA added three new entries to the Known Exploited Vulnerabilities catalog based on evidence of active exploitation: ownCloud improper authentication (CVE-2023-49105), an unspecified Linux kernel vulnerability (CVE-2026-53362), and JFrog Artifactory improper path restriction (CVE-2026-66384). KEV listing confirms these flaws are being exploited in the wild rather than posing theoretical risk. Under BOD 26-04, federal civilian executive branch agencies must prioritize remediation of KEV entries.