Catalog analysis: CISA added this entry on August 26, 2026. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. This site’s publication date is shown separately. Check current vendor guidance before acting.
What the vulnerability is
CVE-2021-23758 is a deserialization of untrusted data vulnerability (CWE-502) affecting Ajax.NET Professional (AjaxPro). This flaw allows for the potential execution of arbitrary code on the host system via the use of arbitrary .NET classes during the deserialization process.
Exposure and applicability
This vulnerability affects environments utilizing the Ajax.NET Professional library. Because this is a third-party library, it may be embedded within various proprietary applications or custom implementations.
Exposure risk is highest for assets where the affected library is internet-facing. Organizations should prioritize identification of all instances of AjaxPro across their infrastructure, noting that some versions of the product may have already reached end-of-life (EoL) or end-of-service (EoS) status.
Remediation priorities
Based on our analysis, remediation should be prioritized according to asset exposure and support status:
- Immediate Mitigation: For supported versions, apply vendor-provided mitigations immediately.
- Lifecycle Transition: For assets running EoL or EoS versions where official patches are unavailable, the priority is to discontinue use of the library or transition to a currently supported version.
- Exposure Reduction: Identify and isolate internet-facing assets utilizing this library to reduce the immediate attack surface while patching or migration occurs.
How to validate remediation
Verification must go beyond confirming a version number, as a deployed fix does not inherently guarantee that the vulnerability is neutralized in a specific environment.
Defenders should verify remediation by:
* Configuration Audit: Confirming that vendor-recommended mitigations are active and correctly configured across all identified instances.
* Dependency Analysis: Validating that EoL versions have been fully removed from production binaries and replaced with supported alternatives.
* Exposure Testing: Using authorized security validation tools to confirm that the specific deserialization path is no longer reachable or exploitable on the network.
Limits and open questions
There are significant limitations regarding the long-term security of this component. If an organization is using a version that is EoL/EoS, there may be no official vendor patch available, leaving the system permanently exposed unless the library is replaced entirely.
Additionally, while CISA has added this to the Known Exploited Vulnerabilities catalog, it remains unknown if this vulnerability is currently being utilized by specific ransomware campaigns. Residual risk remains for any environment where legacy libraries are maintained without active vendor support.
Source and editorial note
CVE-2021-23758: Ajax.NET Professional Deserialization of Untrusted Data Vulnerability · Source date: August 26, 2026 · Retrieved August 31, 2026.
Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.
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