CVE-2021-23758: Deserialization of Untrusted Data

In CISA’s Known Exploited Vulnerabilities catalog: Ajax.NET Professional Deserialization of Untrusted Data Vulnerability.

Added 2026-08-26, federal remediation due 2026-09-09. Known ransomware use: Unknown.

Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.