ownCloud Improper Authentication Vulnerability (CVE-2023-49105)

Catalog analysis: CISA added this entry on August 27, 2026. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. This site’s publication date is shown separately. Check current vendor guidance before acting.

What the vulnerability is

CVE-2023-49105 is an improper authentication vulnerability (CWE-287) affecting ownCloud. The flaw allows an unauthenticated attacker to access, modify, or delete any file within the system. This action is possible provided the attacker knows the victim’s username and the targeted user has not configured a signing key.

Exposure and applicability

This vulnerability does not affect all ownCloud installations equally. Applicability depends on two specific conditions being met simultaneously:
1. User Configuration: The target account must lack a configured signing key.
2. Attacker Knowledge: The attacker must possess the username of the victim.

Infrastructure owners should prioritize assets with high internet exposure and those hosting users who have not implemented signing keys, as these represent the primary attack surface for this flaw.

Remediation priorities

Based on our analysis, defenders should prioritize the following actions to reduce exposure:

• Immediate Patching: Apply mitigations according to vendor instructions. Given its inclusion in CISA’s Known Exploited Vulnerabilities (KEV) catalog, this should be treated as a high-priority update.
• Configuration Audit: Identify users who lack signing keys, as these accounts are the specific targets for this authentication bypass.
• Exposure Reduction: Evaluate whether ownCloud instances are unnecessarily exposed to the public internet, which increases the likelihood of an attacker attempting to leverage known usernames.

How to validate remediation

Verifying that a vulnerability is mitigated requires more than confirming a software version update. To ensure exposure is actually reduced, defenders should:

• Verify Configuration State: Confirm that signing keys are correctly configured for the user base, as the absence of these keys is a prerequisite for the exploit.
• Validate Patch Application: Use vendor-provided tools or documentation to confirm the specific security update addressing CVE-2023-49105 is active on the production environment.

Confirmation of a version number alone does not prove mitigation if the underlying configuration (signing keys) remains in a vulnerable state.

Limits and open questions

There are several unknowns regarding this vulnerability. It is currently unknown whether this flaw has been utilized by ransomware campaigns. Additionally, while vendor instructions provide the path to remediation, the specific level of residual risk for users who cannot implement signing keys—even after patching—should be evaluated against the organization’s internal risk tolerance.

Source and editorial note

CVE-2023-49105: ownCloud Improper Authentication Vulnerability · Source date: August 27, 2026 · Retrieved August 31, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

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