Ajax.NET Professional Deserialization of Untrusted Data Vulnerability

Technical Analysis

CVE-2021-23758 stems from unsafe deserialization within AjaxPro's request-handling logic, which fails to validate or restrict the types of .NET objects it deserializes from client-supplied input. An attacker can craft a malicious serialized payload referencing arbitrary .NET classes, triggering unintended object instantiation and method execution, leading to remote code execution on the underlying IIS/.NET server. Because the product is EoL/EoS, no official patch exists, and organizations must rely on mitigations such as web application firewalls, network segmentation, or migration to supported frameworks. Exploitation typically targets internet-facing ASP.NET applications using legacy AjaxPro components in .ashx handlers. If an AI agent framework or RAG pipeline runs on a legacy .NET web stack incorporating AjaxPro for AJAX callback functionality, successful exploitation could grant attackers code execution on the host, exposing API keys, model credentials, and agent orchestration logic used by the system.

Affected Systems

Ajax.NET Professional (AjaxPro) library, all versions vulnerable to unsafe deserialization; typically deployed within legacy ASP.NET web applications running on IIS servers; end-of-life/end-of-service status confirmed with no vendor patch available.

Indicators of Compromise

• No specific hashes, IPs, or domains published; indicators are context-dependent on exploitation via crafted HTTP requests to AjaxPro .ashx endpoints

Remediation Steps

1. 1

   Discontinue Use of AjaxPro

   Migrate away from Ajax.NET Professional to a supported, actively maintained AJAX/web framework given its EoL/EoS status.

2. 2

   Deploy Compensating Controls

   If immediate migration is not possible, implement WAF rules to block malicious deserialization payloads and restrict access to AjaxPro endpoints.

3. 3

   Network Segmentation

   Isolate legacy systems running AjaxPro from sensitive internal networks and critical infrastructure, including systems supporting AI agent operations.

4. 4

   Monitor for Exploitation

   Review IIS/ASP.NET logs for anomalous POST requests to .ashx handlers and unexpected process spawning from web server processes.

5. 5

   Credential Rotation

   If compromise is suspected, rotate all credentials and API keys accessible from the affected host, particularly those used by any co-located AI agent or automation services.