Critical ownCloud flaw under attack (CVE-2023-49103)

CVE-2023-49103 is an unauthenticated information disclosure flaw in ownCloud's graphapi app (0.2.x before 0.2.1 and 0.3.x before 0.3.1), which ships a third-party GetPhpInfo.php page that returns the full PHP phpinfo output when its URL is requested. An attacker with no credentials or user interaction simply accesses that URL over the network, and the phpinfo output reveals all of the webserver's environment variables plus other potentially sensitive configuration details. In containerized deployments these environment variables frequently include the ownCloud admin password, mail server credentials, and license key, giving attackers direct credentials for the server; notably, disabling the graphapi app does not remove the exposed file. Affected deployments are ownCloud installations running the vulnerable graphapi versions, especially ownCloud Docker images built after February 2023, while containers built before February 2023 are not vulnerable to the credential disclosure. Exploitation is confirmed in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2023-11-30, the EPSS score is 78.4% (top percentile), and public reporting says threat actors have begun exploiting the flaw, though no public PoC is known.

Do: Upgrade the graphapi app to version 0.2.1 or 0.3.1, and note that simply disabling the app is not sufficient — ensure the GetPhpInfo.php file is removed per vendor instructions. Operators of containerized ownCloud deployments (Docker images from February 2023 onward) should assume the ownCloud admin password, mail server credentials, and license key were exposed, rotate them, and review web logs for requests to the GetPhpInfo.php URL. CISA KEV requires applying vendor mitigations or discontinuing use of the product if mitigations are unavailable.

An issue was discovered in ownCloud owncloud/oauth2 before 0.6.1, when Allow Subdomains is enabled. An attacker is able to pass in a crafted redirect-url that bypasses validation, and consequently allows an attacker to redirect callbacks to a Top Level Domain controlled by the attacker.

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.