CVE-2021-23758 Ajax.NET Professional Ajax.NET Professional: unsafe data loading
In plain words: The program unpacks saved data from outside without checking it is safe. Usually lets an attacker run code on the server.
Confirmed exploited by CISA on · US federal patch deadline Sep 9, 2026
What to do
- Install Ajax.NET Professional's security update for Ajax.NET Professional. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
- Product
- Ajax.NET Professional Ajax.NET Professional
- CISA description
- 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.
- Type of flaw
- Unsafe data loading (CWE-502)
- Confirmed exploited
- Aug 26, 2026
- US federal patch deadline
- Sep 9, 2026
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Answering about CVE-2021-23758 ·
Questions about CVE-2021-23758
Is CVE-2021-23758 being exploited?
Yes. CISA added CVE-2021-23758 to its Known Exploited Vulnerabilities catalog on Aug 26, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2021-23758?
Install Ajax.NET Professional's security update for Ajax.NET Professional. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2021-23758?
Only if you use Ajax.NET Professional Ajax.NET Professional. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.