CVE-2021-23758
Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 9 September 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 83.63% probability · 100th percentile
- CISA KEV
- Listed 26 August 2026 · due 9 September 2026
- Weakness
- CWE-502
- Affected
- ajaxpro.2 project/ajaxpro.2 · michaelschwarz/ajax.net professional
- Source
- report@snyk.io
CISA notes
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. 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
References
- http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.htmlExploit, VDB Entry
- https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57Patch, Third Party Advisory
- https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971Third Party Advisory
- http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.htmlExploit, VDB Entry
- https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57Patch, Third Party Advisory
- https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971Third Party Advisory
- https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/Exploit, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.