CVE-2022-39339 is a vulnerability identified in the user_oidc OpenID Connect user backend for Nextcloud, specifically affecting versions prior to 1.2.1. The core issue involves the cleartext transmission of sensitive information, including OIDC client credentials and tokens, over HTTP without the protection of TLS encryption. This vulnerability falls under CWE-319, which concerns the exposure of sensitive data due to unencrypted communication channels. When user_oidc is configured to communicate over plain HTTP, any attacker with network access capable of monitoring traffic—such as those on the same local network, compromised routers, or ISP-level surveillance—could intercept these credentials and tokens. This interception could lead to unauthorized access to user accounts or broader Nextcloud instances. The vulnerability does not require user interaction beyond normal usage and does not require authentication to exploit, as it targets the transmission channel itself. The issue was addressed in user_oidc version 1.2.1 by enforcing or recommending the use of HTTPS for all communications. Users who cannot upgrade are advised to configure Nextcloud to use HTTPS by setting an HTTPS discovery URL in the OIDC provider settings, ensuring that sensitive tokens and credentials are transmitted securely. No known exploits in the wild have been reported, but the risk remains significant due to the nature of the data exposed and the ease of interception in unencrypted networks.

For European organizations, the impact of this vulnerability can be substantial, especially for those relying on Nextcloud for collaboration, file sharing, and identity management. The exposure of OIDC client credentials and tokens could lead to unauthorized access to sensitive corporate data, user impersonation, and potential lateral movement within networks. This risk is heightened in environments with shared or public networks, such as universities, co-working spaces, or enterprises with remote workers using unsecured Wi-Fi. Compromise of authentication tokens could also undermine trust in federated identity systems, leading to broader security incidents. Given the widespread adoption of Nextcloud in Europe, particularly among public sector entities, educational institutions, and SMEs seeking open-source cloud solutions, the vulnerability could affect a significant number of users. Additionally, the GDPR framework imposes strict data protection requirements, and a breach resulting from this vulnerability could lead to regulatory penalties and reputational damage. The absence of known exploits reduces immediate risk but does not eliminate the potential for targeted attacks, especially by threat actors monitoring unencrypted traffic in strategic sectors.

To mitigate this vulnerability, European organizations should prioritize upgrading the user_oidc backend to version 1.2.1 or later, which includes fixes to enforce secure transmission. For environments where immediate upgrading is not feasible, administrators must ensure that Nextcloud is accessed exclusively over HTTPS by configuring an HTTPS discovery URL in the OIDC provider settings. This configuration change forces the use of TLS, preventing cleartext transmission of sensitive tokens and credentials. Network administrators should also implement network-level protections such as enforcing HTTPS via HSTS policies, deploying network segmentation to limit exposure of sensitive traffic, and monitoring network traffic for unencrypted OIDC communications. Additionally, organizations should audit their Nextcloud configurations and user_oidc versions regularly, integrate vulnerability scanning into their patch management processes, and educate users about the risks of using unsecured networks. Deploying endpoint security solutions capable of detecting anomalous authentication token usage can further reduce risk. Finally, organizations should consider deploying network intrusion detection systems (NIDS) tuned to detect suspicious OIDC traffic patterns indicative of interception or replay attacks.