CVE-2021-23758
CriticalExploitedPublic exploitRemote Code Execution in AjaxNetProfessional
Published Dec 7, 2021 · Updated Sep 10, 2026 · Also known as GHSA-6r7c-6w96-8pvw, GHSA-74r6-grj9-8rq6, SNYK-DOTNET-AJAXPRO2-1925971
Key Facts
Patch immediately- CVE-2021-23758 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting AjaxPro.2 (Ajaxpro.2 Project), Ajax.net Professional (Michaelschwarz), AjaxNetProfessional (nuget).
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Aug 20, 2026. Public exploit code is available.
- EPSS estimates a 83% probability of exploitation in the next 30 days.
- Fixed versions are available, including AjaxNetProfessional 21.11.29.1, AjaxPro.2 unspecified, AjaxPro.2 21.10.30.1.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
83%
Higher than 99.6% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-23758 brief as a PDF
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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.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Aug 26, 2026 | Sep 9, 2026 | Not reported |
| Industry KEV feed | Aug 20, 2026 | Sep 9, 2026 | Not reported |
| CIRCL KEV | Aug 26, 2026 | Sep 9, 2026 | Not reported |
| ENISA EUVD | Aug 26, 2026 | n/a | Not reported |
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.
Affected Products
4 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| AjaxPro.2Ajaxpro.2 Project | See advisory | 21.10.30.1 |
| Ajax.net ProfessionalMichaelschwarz | See advisory | 21.10.30.1 |
| AjaxNetProfessionalnuget | See advisory | 21.11.29.1 |
Patched Releases
AjaxNetProfessional
21.11.29.1
AjaxPro.2
unspecified, 21.10.30.1
Ajax.net Professional
21.10.30.1
Timeline
Publicly disclosed
Dec 7, 2021
Added to Industry KEV feed
Aug 20, 2026
Added to CISA KEV
Aug 26, 2026
Added to CIRCL KEV
Aug 26, 2026
Added to ENISA EUVD
Aug 26, 2026
Last updated
Sep 10, 2026
Weakness Type
- CWE-502 Deserialization of Untrusted Data
References
- advisoryGHSA advisory
- advisoryGHSA advisory
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2021-23758
- exploitMSF ajaxpro_deserialization_rce.rb
- exploitVulnCheck exploitation report
FAQ
Common Questions.
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.
Affected: AjaxPro.2 (Ajaxpro.2 Project); Ajax.net Professional (Michaelschwarz); AjaxNetProfessional (nuget). The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Aug 20, 2026.
Yes. It was added on Aug 26, 2026 with a federal remediation due date of Sep 9, 2026.
Public exploit code is available.
Fixed versions are available, including AjaxNetProfessional 21.11.29.1, AjaxPro.2 unspecified, AjaxPro.2 21.10.30.1.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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