CVE-2017-0883 : Security Advisory and Response

CVE-2017-0883 was published on April 5, 2017, and affects Nextcloud Server versions prior to 9.0.55 and 10.0.2. The vulnerability allows an authenticated attacker to escalate permissions when re-sharing files through the OCS API, potentially leading to unauthorized file modifications.

Understanding CVE-2017-0883

This CVE entry highlights a permission escalation issue in Nextcloud Server versions before 9.0.55 and 10.0.2, impacting the security of shared files.

What is CVE-2017-0883?

The vulnerability in Nextcloud Server versions prior to 9.0.55 and 10.0.2 enables an attacker to increase their permissions when re-sharing files via the OCS API. By exploiting this flaw, an authenticated adversary can elevate their access level and potentially manipulate shared files beyond their authorized permissions.

The Impact of CVE-2017-0883

The vulnerability allows an attacker with read-only access to shared files to modify them, posing a significant security risk to the confidentiality and integrity of sensitive data stored on affected Nextcloud Servers.

Technical Details of CVE-2017-0883

This section delves into the specific technical aspects of the CVE.

Vulnerability Description

The issue arises from a permission-related flaw within the OCS sharing API, enabling attackers to reshare files with increased permission levels, leading to unauthorized file modifications.

Affected Systems and Versions

Product: Nextcloud Server
Vendor: Nextcloud
Versions Affected: All versions before 9.0.55 and 10.0.2

Exploitation Mechanism

The vulnerability allows an authenticated attacker to exploit the OCS API to escalate their permissions when re-sharing files, granting them unauthorized access to modify shared files.

Mitigation and Prevention

Protecting systems from CVE-2017-0883 requires immediate actions and long-term security practices.

Immediate Steps to Take

Update Nextcloud Server to version 9.0.55 or 10.0.2 to mitigate the vulnerability.
Monitor file permissions and access controls to detect unauthorized modifications.

Long-Term Security Practices

Regularly audit and review file sharing permissions to prevent unauthorized access.
Educate users on secure file sharing practices and the importance of maintaining permission integrity.

Patching and Updates

Apply security patches and updates provided by Nextcloud to address known vulnerabilities and enhance system security.