Ajax.NET Professional's Deserialization of Untrusted Data Allows Unauthenticated Remote Attackers to Execute Arbitrary Code via a Crafted Serialized Object; CISA's September 9th KEV Deadline Has Passed

Last refreshed2026-09-27

Status: KEV | Advisory ID: CVE-2021-23758

Key Details

CVE	CVE-2021-23758
Vulnerability Name	Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
CVSS Score / Version	8.1 (High) / CVSS v3.1
Updated	2026-09-22
CVSS Vector	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`
CVSS Prose	attack vector is network; attack complexity is high; privileges required is none; user interaction is none; scope is unchanged; confidentiality impact is high; integrity impact is high; availability impact is high.
Affected products	Ajax.NET Professional Ajax.NET Professional, ajaxpro.2_project ajaxpro.2, and michaelschwarz Ajax.NET Professional
Exploitation status	Listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating confirmed active exploitation.
Classified as	CWE-502 (Deserialization of Untrusted Data)
KEV listing	Added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2026-08-26.
Exploitation prediction (EPSS)	82.58% probability of exploitation in the next 30 days (100% percentile) -- FIRST.org's EPSS model.
Federal remediation deadline	2026-09-09 (CISA KEV, Binding Operational Directive).

Affected Products, Subsystems & Sectors

Vendor	Product	Affected Versions	Patch Status
Ajax.NET Professional	Ajax.NET Professional
ajaxpro.2_project	ajaxpro.2
michaelschwarz	Ajax.NET Professional

Vendor

Product

Affected Versions

Patch Status

Ajax.NET Professional

ajaxpro.2_project

ajaxpro.2

michaelschwarz

Ajax.NET Professional

Subsystems	General OT
Sectors	Multiple

What to Know

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.

What to Do

Monitor Ajax.NET Professional, ajaxpro.2_project, and michaelschwarz's web pages for any future patch releases.

References

Source	Reference
NVD	https://nvd.nist.gov/vuln/detail/CVE-2021-23758
CVE	https://www.cve.org/CVERecord?id=CVE-2021-23758

Source

Reference

NVD

https://nvd.nist.gov/vuln/detail/CVE-2021-23758

CVE

https://www.cve.org/CVERecord?id=CVE-2021-23758

KEV Required Action

Field	Value
KEV Link	https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Date Added to KEV	2026-08-26
Required Action Due Date	2026-09-09
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.

Field

Value

KEV Link

https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Date Added to KEV

2026-08-26

Required Action Due Date

2026-09-09

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.