EUVD-2026-9920

Comprehensive Technical Analysis of EUVD-2026-9920

1. Vulnerability Assessment and Severity Evaluation

The vulnerability described in EUVD-2026-9920 affects OpenClaw's Nextcloud Talk plugin versions prior to 2026.2.6. The issue arises from the plugin's acceptance of equality matching on the mutable actor.name display name field for allowlist validation. This flaw allows attackers to bypass direct message (DM) and room allowlists by changing their display name to match an allowlisted user ID, thereby gaining unauthorized access to restricted conversations.

Severity Evaluation:

• Base Score: 9.3
• Base Score Version: 4.0
• Base Score Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

The high base score of 9.3 indicates a critical vulnerability. The CVSS vector highlights that the attack can be executed remotely (AV:N), requires low complexity (AC:L), and does not need any special privileges (PR:N) or user interaction (UI:N). The impact on confidentiality, integrity, and availability is high (VC:H, VI:H, VA:H), making this a severe issue.

2. Potential Attack Vectors and Exploitation Methods

Attack Vectors:

• Display Name Spoofing: An attacker can change their Nextcloud display name to match an allowlisted user ID.
• Unauthorized Access: By spoofing the display name, the attacker can gain access to restricted conversations, bypassing the allowlist mechanism.

Exploitation Methods:

• Social Engineering: Attackers may use social engineering techniques to gather information about allowlisted user IDs.
• Automated Scripts: Attackers could write scripts to automate the process of changing display names and attempting to join restricted conversations.

3. Affected Systems and Software Versions

Affected Software:

• OpenClaw's Nextcloud Talk plugin versions prior to 2026.2.6

Affected Systems:

• Any system running the vulnerable versions of the Nextcloud Talk plugin.
• Organizations and individuals using Nextcloud for secure communication and collaboration.

4. Recommended Mitigation Strategies

Immediate Actions:

• Update Software: Upgrade to Nextcloud Talk plugin version 2026.2.6 or later.
• Temporary Workaround: Disable the allowlist feature until the software is updated.

Long-Term Mitigation:

• Regular Patching: Implement a regular patching and update schedule for all software components.
• Monitoring: Enhance monitoring and logging to detect unusual changes in display names and unauthorized access attempts.
• User Education: Educate users about the risks of display name spoofing and the importance of reporting suspicious activities.

5. Impact on European Cybersecurity Landscape

The vulnerability poses a significant risk to organizations and individuals relying on Nextcloud for secure communication. The potential for unauthorized access to sensitive conversations can lead to data breaches, loss of confidential information, and reputational damage. Given the widespread use of Nextcloud in Europe, this vulnerability underscores the need for robust cybersecurity practices and timely patch management.

6. Technical Details for Security Professionals

Vulnerability Details:

• CWE ID: CWE-284 (Improper Access Control)
• Exploitability: The vulnerability can be exploited by changing the display name to match an allowlisted user ID, which is a relatively simple process.

Detection and Response:

• Detection: Implement intrusion detection systems (IDS) to monitor for unusual changes in display names and access patterns.
• Response: Develop an incident response plan that includes steps for identifying and mitigating unauthorized access attempts.

References:

• GitHub Advisory
• GitHub Commit
• VulnCheck Advisory

Aliases:

• CVE-2026-28474

Assigner:

• VulnCheck

ENISA IDs:

• Product: [{"id":"d2194348-aa4c-360e-bd85-cba39dc878ae","product":{"name":"nextcloud-talk"},"product_version":"0 <2026.2.6"}]
• Vendor: [{"id":"a01e5023-65f7-3c3c-b507-a9eb31c57e4c","vendor":{"name":"OpenClaw"}}]

By addressing this vulnerability promptly and implementing robust security measures, organizations can mitigate the risk of unauthorized access and protect their sensitive communications.