Exploited vulnerability · CISA KEV

Is CVE-2021-23758 exploited? Yes: in CISA KEV since 26 Aug 2026

Gociux · Ajax.NET Professional · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-23758, Ajax.NET Professional Deserialization of Untrusted Data Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 26 Aug 2026, 1727 days after it was published. It affects Ajax.NET Professional. If you run it, CISA's required action is: 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.

What it is

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

1. Check whether you run it. Look for Ajax.NET Professional in your asset inventory, including appliances and cloud images. Stack check lists every exploited Ajax.NET Professional CVE at once.
2. Apply the fix. 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.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 3 Dec 2021.
4. Get told next time. Email alerts when CISA adds a CVE for Ajax.NET Professional.

References

• nvd.nist.gov/vuln/detail/CVE-2021-23758

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in August 2026 · act-now radar.