CVE-2021-23758
Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
Ajax.NET Professional Ajax.NET Professional
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.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 26 August 2026. US federal agencies were required to remediate it by 9 September 2026.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 83.6%, which is higher than 99.7% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2021-23758 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2021-23758.
What does CVE-2021-23758 affect?
CVE-2021-23758 affects Ajax.NET Professional Ajax.NET Professional. 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.
How severe is CVE-2021-23758?
CVE-2021-23758 is rated HIGH with a CVSS base score of 8.1. EPSS puts the probability of exploitation in the next 30 days at 83.6%, higher than 99.7% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 9 September 2026.
How should organisations respond to CVE-2021-23758?
Apply the vendor patch for Ajax.NET Professional Ajax.NET Professional as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.