---
id: "CVE-2021-23758"
kind: "vulnerability"
aliases: ["CVE-2021-23758"]
title: "All versions of package ajaxpro.2 are vulnerable to Deserialization of Untrusted Data due to the possibility of\u2026"
severity: "critical"
cvss: 9.8
epss: null
exploited: true
status: "open"
category: "package"
products: [{"name": "Ajax.NET Professional Ajax.NET Professional", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "ajaxpro.2 project ajaxpro.2", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "michaelschwarz ajax.net professional", "fixed": ["21.10.30.1"], "affected": "< 21.10.30.1", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["ajax.net-professional", "asp.net", "dotnet", "exploited", "package"]
not_affected_if: ["not-using-ajaxpro"]
published_at: "2021-12-03T20:15:07+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:52+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-23758", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-23758", "first_seen_at": "2026-10-23T23:44:52+00:00"}]
---

# All versions of package ajaxpro.2 are vulnerable to Deserialization of Untrusted Data due to the possibility of…

Ajax.NET Professional (AjaxPro), a .NET library for calling server methods from JavaScript, deserializes untrusted data and lets remote attackers instantiate arbitrary .NET classes. That gives an attacker remote code execution on the server.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Ajax.NET Professional Ajax.NET Professional affected ? fixed ?
- vendor:ajaxpro.2 project ajaxpro.2 affected ? fixed ?
- vendor:michaelschwarz ajax.net professional affected < 21.10.30.1 fixed 21.10.30.1

## How to check

Search your .NET solution and deployed bins for AjaxPro.dll or the Ajax.NET Professional package reference in .csproj/packages.config.

## Fix

Discontinue use of Ajax.NET Professional and move to a supported AJAX or web API approach; the product is end-of-life and no fixed version is listed in the sources.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-23758
- 2026-10-23T23:44:52+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-23758

## From the sources

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.

CISA 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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_