CVE-2021-23758Known exploitationPublic exploitNetwork attack vector

Unauthenticated code execution via unrestricted type instantiation

Published Dec 3, 2021 · Updated Aug 27, 2026

Unsafe JSON deserialization in Ajax.NET Professional 21.11.29 and earlier allows remote attackers to execute arbitrary code via HTTP requests. JavaScriptDeserializer.DeserializeCustomObject passes a client-supplied __type value to Activator.CreateInstance without first restricting the requested .NET class. No authentication or user interaction is required, but exploitation depends on a reachable AjaxPro HTTP handler and a usable gadget class in the host application.

CVSS severity8.1
High
EPSS probability83.63%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Unsafe JSON deserialization in Ajax.NET Professional 21.11.29 and earlier allows remote attackers to execute arbitrary code via HTTP requests. JavaScriptDeserializer.DeserializeCustomObject passes a client-supplied __type value to Activator.CreateInstance without first restricting the requested .NET class. No authentication or user interaction is required, but exploitation depends on a reachable AjaxPro HTTP handler and a usable gadget class in the host application.

The record

CVE
CVE-2021-23758
Published
Dec 3, 2021
Updated
Aug 27, 2026
Vendor
Michael Schwarz
Product
Ajax.NET Professional
Classifications
CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <unspecified

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michael Schwarz · Ajax.NET Professionalversion=0 <unspecified

Published CVSS scores

8.1SnykCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo