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[ CVE-2021-23758 · Published 3 Dec 2021 ]

Ajax.NET Professional Deserialization of Untrusted Data Vulnerability

Exploited · CISA KEV CVSS 9.8 EPSS 83%Fix available

[ Why it matters ]Priority signals

  • Exploited in the wild: on CISA's Known Exploited Vulnerabilities list since 2026-08-26
  • EPSS: 83% chance of exploitation in the next 30 days (higher than 100% of CVEs)
  • Critical severity: CVSS 9.8

[ Description ]Official description

All versions of package ajaxpro.2 are vulnerable to Deserialization of Untrusted Data due to the possibility of deserialization of arbitrary .NET classes, which can be abused to gain remote code execution.

CISA: Ajax.NET Professional (AjaxPro) contains a deserialization of untrusted data vulnerability that could allow for remote code execution via arbitrary .NET classes. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

[ Fixes ]Fixes and patches

CISA required action (US federal deadline 9 Sep 2026): 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.

[ References ]References