CVE-2021-23758: Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
What it is
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.
What to do
Treat this as urgent. Identify every affected system, starting with anything internet-facing, and apply the vendor fix or mitigation within days. If you cannot patch quickly, isolate or disable the affected service and watch for signs of compromise.
- Priority
- Act now: Patch or mitigate internet-facing systems within days.
- Severity (CVSS)
- 8.1 high
- CISA assessment (SSVC)
- actively exploited; needs manual effort per target; total control of the affected system
- Exploit probability (EPSS, 30 days)
- 83%, in the top 1% of all CVEs
- Added to CISA KEV
- 26 August 2026
- CISA fix-by date
- 9 September 2026 (US federal agencies; a sensible deadline for everyone)
- Ransomware use
- Not known
- Weakness
- CWE-502
References
- NIST NVD entry
- CISA KEV entry
- github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a
- snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971
- github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a
- snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971
Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.