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CVE-2021-23758

Ajax.NET Professional Deserialization of Untrusted Data

8.1 HIGHActively exploited (CISA KEV)Public exploitEPSS 82.6%
  1. Published3 Dec 2021
  2. Added to CISA KEV26 Aug 2026
  3. Remediation due9 Sept 2026
Actively exploited (CISA KEV)

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.

Added to KEV: 26 Aug 2026Federal remediation due: 9 Sept 2026

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Ajaxpro.2all versions
Michaelschwarz Ajax.net Professional< 21.10.30.1

Remediation

Fixed in
Michaelschwarz Ajax.net Professional≥ 21.10.30.1

References

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Frequently asked

Is CVE-2021-23758 being actively exploited?

Yes. CVE-2021-23758 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 26 Aug 2026.

How severe is CVE-2021-23758?

CVE-2021-23758 has a CVSS 3.1 base score of 8.1, rated high. EPSS estimates a 82.6% probability of exploitation.

Which products are affected by CVE-2021-23758?

Affected products include Ajaxpro.2, Michaelschwarz Ajax.net Professional.

How do I fix CVE-2021-23758?

Upgrade affected software to a fixed version, for example Michaelschwarz Ajax.net Professional 21.10.30.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-23758 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, a risk for it never ranks below high, and the update that fixes it moves to the Emergency patch lane. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.