CVE-2026-26222 – DocLink .NET Remoting Unauthenticated Arbitrary File Read/Write RCE

Identify and Isolate Affected Systems: Immediately identify all systems running the vulnerable software component. Disconnect or logically segment these systems from the production network if possible without causing critical business disruption. If full isolation is not feasible, restrict network access to only essential services and trusted sources.

Block Known Malicious Indicators: If any indicators of compromise (IOCs) such as malicious IP addresses, URLs, or file hashes are identified through threat intelligence feeds or initial incident response, implement immediate blocks at the perimeter firewall, WAF, or network intrusion prevention systems (NIPS).

Implement Emergency WAF Rules: Configure Web Application Firewalls (WAFs) or API Gateways to block requests containing known exploitation patterns. For a deserialization vulnerability, this might involve blocking requests with specific header values, content types, or payload structures that are indicative of malicious serialized objects. Consult vendor-specific guidance if available.

Review Logs for Exploitation Attempts: Scrutinize web server access logs, application logs, and system event logs for any signs of exploitation. Look for unusual requests, unexpected process creation, outbound connections from the affected server, or modifications to critical system files. Prioritize logs from the period immediately preceding and following the public disclosure of the CVE.

Prepare for Patch Deployment: If an emergency patch is released, begin preparations for its immediate deployment. This includes reviewing the patch documentation, identifying necessary prerequisites, and preparing rollback plans. Do not deploy without proper testing, but expedite the testing process.

2. PATCH AND UPDATE INFORMATION

Monitor Vendor Advisories: Continuously monitor official vendor security advisories, mailing lists, and support channels for the release of an official patch or updated software version that addresses CVE-2026-26222. Subscribe to security notifications from the relevant software vendor.

Apply Official Patches Promptly: Once an official patch or updated version is released, prioritize its application across all affected systems. Follow the vendor's recommended patching procedure, which typically involves:
a. Backing up critical data and configurations.
b. Testing the patch in a non-production environment to ensure compatibility and stability.
c. Scheduling a maintenance window for production deployment.
d. Applying the patch to production systems.
e. Verifying the successful installation and operational stability post-patch.

Prioritize Critical Systems: Deploy patches first to internet-facing systems, systems handling sensitive data, and those critical to business operations, as these present the highest risk.

Verify Patch Application: After applying the patch, verify that the vulnerability is no longer present. This can be done through vulnerability scanning, manual checks (e.g., version numbers), or attempting to reproduce the exploit in a controlled test environment.

3. MITIGATION STRATEGIES

Disable Insecure Deserialization: If the application allows deserialization of untrusted data, and a patch is not immediately available, consider disabling the feature entirely if it is not critical for core application functionality. This may require code changes or configuration adjustments within the application or framework.

Implement Deserialization Allow-listing: If deserialization cannot be entirely disabled, implement a strict allow-list for classes that are permitted to be deserialized. This prevents an attacker from deserializing arbitrary malicious classes. This typically requires modifying application code or configuration to specify a safe set of classes.

Restrict Network Access: Implement network segmentation and firewall rules to limit direct access to the vulnerable service or application. Allow connections only from trusted internal networks, specific IP addresses, or through well-secured gateways (e.g., reverse proxies, VPNs).

Implement Least Privilege: Ensure the application or service runs with the absolute minimum necessary operating system privileges. This limits the potential impact of a successful exploit, even if remote code execution occurs.

Utilize Application-Level Firewalls (WAFs): Beyond emergency rules, configure WAFs with specific rules to detect and block common deserialization attack patterns, such as unusual content types, unexpected HTTP headers, or large, malformed serialized payloads.

Monitor Network Traffic: Implement deep packet inspection (DPI) and network intrusion detection systems (NIDS) to monitor for suspicious traffic patterns, including attempts to exploit deserialization vulnerabilities or post-exploitation activity (e.g., unusual outbound connections, command-and-control communication).

4. DETECTION METHODS

Log Analysis:
a. Web Server Logs: Monitor for unusual request methods, paths, user-agents, or large/malformed request bodies indicative of exploitation attempts.
b. Application Logs: Look for errors related to deserialization, unexpected class loading, or unusual stack traces.
c. System Logs: Monitor for unexpected process creation, changes to system configurations, or unusual network connections originating from the vulnerable server.
d. Security Event Logs: Integrate logs with a Security Information and Event Management (SIEM) system for centralized analysis and alerting on suspicious activities.

Network Intrusion Detection/Prevention Systems (NIDS/NIPS): Deploy NIDS/NIPS with up-to-date signatures capable of detecting known deserialization exploits or common attack patterns. Monitor alerts generated by these systems closely.

Endpoint Detection and Response (EDR): Utilize EDR solutions on affected servers to monitor for post-exploitation activities such as:
a. Unexpected process execution (e.g., shell commands, script interpreters).
b. File system modifications (e.g., creation of web shells, modification of configuration files).
c. Unusual network connections to external or internal hosts.
d. Privilege escalation attempts.

Vulnerability Scanning: Regularly perform authenticated and unauthenticated vulnerability scans against your applications and infrastructure. Ensure scanners are updated with definitions for CVE-