On CISA’s exploited listownCloud ownCloudOffice, email & file sharing
ownCloud Improper Authentication Vulnerability
- What it is
- ownCloud contains an improper authentication vulnerability that allows an attacker to access, modify, or delete any file without authentication if the username of a victim is known, and the victim has no signing-key configured.
- Who's affected
- Anyone using ownCloud ownCloud.
- Under attack?
- Yes. CISA added this to its catalog of actively exploited vulnerabilities on Aug 27, 2026.
- What to do
- Install the vendor's security update. If there isn't one yet, apply the vendor's workaround, or stop using the product until it's fixed. CISA lists this as actively exploited, so treat it as urgent.
- Fixed in
- See the vendor's advisory
- CISA deadline
- Federal agencies must fix this by Aug 30, 2026. Everyone else should treat that as a ceiling, not a target.
- CISA's instruction
- 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.
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