CVE-2021-23758Ajax.NET Professional Deserialization of Untrusted Data Vulnerability

BOD 26-04 remediation window

With CISA's SSVC answers for this CVE (automatable: no, technical impact: total), BOD 26-04 Table 1 gives 3 days and forensic triage on a publicly exposed asset (row 3) and 14 days on an asset that is not publicly exposed (row 11) ^S06. CISA set the catalogue due date at 14 days; under BOD 26-04 it reflects CISA's own view of whether the flaw sits on publicly exposed assets ^S07. The directive binds US federal civilian executive branch agencies only.

What CISA says

Short description

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.

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.

Notes

This vulnerability affects an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see: https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2021-23758

CWE in the catalogue

CWE-502

Official links

• CISA KEV catalogue entry cisa.gov
• NVD record nvd.nist.gov

Vendor advisory and patch links

References NVD tags Vendor Advisory or Patch, exactly as NVD lists them.

• https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57 Patch, Third Party Advisory

Links in CISA's notes

• https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57
• https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
• https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
• https://nvd.nist.gov/vuln/detail/CVE-2021-23758

NVD details

CWE (NVD)

CWE-502 by nvd@nist.gov

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS versions in NVD

V2, V31

Last modified in NVD

2026-08-27T04:16:38.863

Where each value comes from

This product uses data from the NVD API but is not endorsed or certified by the NVD. CISA does not endorse Sysprobs. Methodology.