Corporate Nextcloud Security Gaps: Default Settings, Antivirus Failures and Open Source Integration Challenges

Nextcloud in corporate environments demands far more than default open source settings to achieve acceptable security levels, according to a detailed technical review published by K2Tech.

The company’s specialist Roma Masyagutov explains that while LDAP integration, antivirus plugins, audit logging and access policies exist, real-world testing often exposes dangerous gaps. A large infected file can still reach storage even when an antivirus solution is supposedly active.

Architecture and Perimeter Defenses

Corporate Nextcloud runs across load balancers, application servers, a MariaDB Galera cluster for metadata, Redis for sessions, S3 object storage and Elasticsearch for logs, all spread across three availability zones. WAF solutions from vendors such as Wallarm and Qrator plus Anti-DDoS services sit in front of the infrastructure. Additional layers include vulnerability scanning with VULS, infrastructure-level SRK, security groups, IAM and CloudTrail logging.

LDAP and Antivirus Integration Issues

Native LDAP plugins connect reliably to corporate Active Directory, automatically mapping groups and permissions. Antivirus integration, however, proves far more fragile. When the antivirus service becomes unreachable, the Antivirus for files plugin simply uploads the file to S3 without scanning. A later parameter avBlockUnreachable was added, yet it functions only with ClamAV and still requires manual configuration for other engines.

Another critical flaw appears during chunked uploads. Files are transferred in 5–10 MB pieces and reassembled with a MOVE command. Older plugin versions checked only individual PUT requests, leaving the final assembled file unexamined. Administrators must update the plugin and align chunk sizes with the antivirus stream length using commands such as occ config:app:set files max_chunk_size --value="104857600".

Comparing Three Antivirus Engines

Three ICAP-based engines were evaluated on identical hardware: ClamAV, Kaspersky Scan Engine and PT Sandbox.

• ClamAV offers open source signature-based detection but lacks built-in clustering, web panels and monitoring; administrators must build these capabilities themselves.
• Kaspersky Scan Engine provides a web console, native clustering via shared database and integration with SIEM systems, delivering the fastest inline scanning speeds in tests.
• PT Sandbox combines signature detection with behavioral analysis yet proved the most resource-intensive, with load averages reaching 115 during sequential uploads.

Throughput measurements for 30 MB and 100 MB files containing EICAR signatures showed Kaspersky Scan Engine consistently outperforming the others, while PT Sandbox imposed the highest CPU overhead even without behavioral analysis enabled.

The authors conclude that antivirus scanning in a Nextcloud pipeline must be treated as a dedicated service whose failure modes, monitoring, high-availability design and re-scan policies require careful engineering. Frequent Nextcloud releases and plugin updates further necessitate ongoing regression testing on staging environments before production rollout.