CVEs / CVE-2021-23758
CVE-2021-23758: Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
- Known exploited in the CISA KEV catalog since 26 Aug 2026
- critical 9.8 CVSS 3.1 (NVD)
- EPSS 82.5% chance of exploitation in the next 30 days, higher than 99% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
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.
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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| n/a AjaxPro.2 | before unspecified | unspecified |
| Product | Affected | Fixed in |
|---|---|---|
| AjaxNetProfessional (NuGet) | before 21.11.29.1 | 21.11.29.1 |
Package versions from GHSA-6r7c-6w96-8pvw.
Exploitation
| In CISA KEV since | 26 Aug 2026 |
|---|---|
| Due date for US federal agencies | 9 Sep 2026 |
| Used in ransomware campaigns | Unknown |
| 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. |
Severity
| CVSS 3.1 | 9.8 criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HScored by NVD |
|---|---|
| Weakness | CWE-502 |
References
- CVE-2021-23758 on NVD
- CVE-2021-23758 in the CISA KEV catalog
- https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57 (cited by CISA)
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk (cited by CISA)
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk (cited by CISA)
- CVE-2021-23758 on OSV
- http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html Exploit, VDB Entry
- https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57 Patch, Third Party Advisory
- https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971 Third 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-2021-23758 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.