CVE-2022-31014 is a medium-severity vulnerability affecting Nextcloud Server versions prior to 22.2.8, versions from 23.0.0 up to but not including 23.0.5, and versions from 24.0.0 up to but not including 24.0.1. Nextcloud is a widely used open-source personal cloud server platform that supports file sharing, collaboration, and communication services. The vulnerability is classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) and CWE-93 (Improper Neutralization of CRLF Sequences), indicating an injection flaw related to improper sanitization of special characters, specifically newline characters, in SMTP commands. The flaw allows an attacker to perform SMTP command injection by exploiting the way Nextcloud handles SMTP communication. By injecting specially crafted input containing newline characters, an attacker can hijack an already authenticated SMTP session and execute arbitrary SMTP commands. This can include sending emails on behalf of the legitimate user, modifying the 'FROM' address, or performing other SMTP operations depending on the backend SMTP server's supported commands and configuration. The impact of this vulnerability depends heavily on the SMTP server's configuration and the commands it supports. Since the attacker leverages an authenticated session, the attack requires that the SMTP credentials are already valid and that the attacker can inject malicious input into the SMTP communication handled by Nextcloud. There are no known workarounds, and the recommended mitigation is to upgrade Nextcloud Server to versions 22.2.8, 23.0.5, or 24.0.1 or later, where the input sanitization has been improved to neutralize newline characters and prevent injection. No known exploits have been observed in the wild as of the published date, but the vulnerability poses a risk of email spoofing, unauthorized email sending, and potential phishing or spam campaigns leveraging compromised SMTP sessions.

For European organizations using Nextcloud Server, this vulnerability could lead to unauthorized use of their email infrastructure, enabling attackers to send fraudulent emails appearing to come from legitimate users. This can undermine trust in internal and external communications, facilitate phishing attacks, and potentially lead to data leakage if sensitive information is sent via email. Organizations relying on Nextcloud for collaboration and communication may face reputational damage and operational disruption if attackers exploit this flaw to spread malware or misinformation. The impact is particularly significant for sectors with strict data protection regulations such as finance, healthcare, and government, where email integrity and confidentiality are critical. Since the attack requires hijacking an authenticated SMTP session, organizations with weak credential management or exposed SMTP credentials are at higher risk. The lack of workarounds means that until patched, affected organizations remain vulnerable. Additionally, misuse of SMTP commands could lead to blacklisting of organizational email domains, affecting legitimate email delivery.

1. Immediate upgrade of Nextcloud Server to versions 22.2.8, 23.0.5, or 24.0.1 or later to ensure the vulnerability is patched. 2. Review and tighten SMTP server configurations to restrict allowed commands and enforce strict input validation on the server side, minimizing the impact of any injection attempts. 3. Implement strong credential management practices, including regular password changes and use of multi-factor authentication for SMTP accounts to reduce the risk of session hijacking. 4. Monitor SMTP logs for unusual command sequences or unexpected email sending patterns that could indicate exploitation attempts. 5. Employ email authentication mechanisms such as SPF, DKIM, and DMARC to detect and mitigate spoofed emails resulting from exploitation. 6. Conduct user awareness training focused on recognizing phishing emails that may arise from this vulnerability exploitation. 7. If upgrading immediately is not feasible, consider isolating Nextcloud SMTP communications within a secure network segment and restricting access to trusted users and systems only.