CVE-2021-23758: Ajax.NET Professional exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

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.

Description quoted from the CVE record (assigned by snyk, published 2021-12-03).

Weakness: CWE-502 Deserialization of Untrusted Data

How it can be exploited

Exploitable over the network with high attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: total.

On CISA KEV since: 2026-08-26
US federal deadline: 2026-09-09
Ransomware use: Not known

Public exploit evidence (Exploit Observer)

Also known as: CNNVD-202112-198, CNVD-2021-95598, EUVD-2021-2466, GHSA-6r7c-6w96-8pvw, GHSA-74r6-grj9-8rq6, SNYK-DOTNET-AJAXPRO2-1925971

VEDAS cluster: VEDAS:BRICKBUNGALOW

Exploit Observer links 3 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (3)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Vulnerability databases and vendor advisories (11)

Catalogue entries, not exploit evidence.

Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2021-2466
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-6r7c-6w96-8pvw
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-74r6-grj9-8rq6
Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23758
Vulnerability database or vendor advisory: https://osv.dev/vulnerability/CVE-2021-23758
Vulnerability database or vendor advisory: https://osv.dev/vulnerability/GHSA-6r7c-6w96-8pvw
Vulnerability database or vendor advisory: https://osv.dev/vulnerability/GHSA-74r6-grj9-8rq6
Vulnerability database or vendor advisory: https://security.snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971
Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758
Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202112-198
Vulnerability database or vendor advisory: https://www.cnvd.org.cn/flaw/show/CNVD-2021-95598

10 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS: 0.826
very likely to be attacked soon
VEDAS: 0.980
strong exploit evidence
On CISA KEV: Yes, since 2026-08-26
Detection rule: Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish. The vertical line is the day CISA added it to its exploited list.

VEDAS flagged this bug about 18 days before CISA confirmed attacks.

Who is affected

Product	Affected	Not affected
AjaxPro.2	before unspecified	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

Exploit Observer also maps it to: ajaxpro.2_project ajaxpro.2.

How to fix it

Fixed versions stated in the CVE record: unspecified.

CISA 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.

Vendor guidance:

How to detect it

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2021-23758 AjaxPro.NET - Deserialization RCE Attempt. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2021-23758 AjaxPro.NET - Deserialization RCE Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/ajaxpro/"; nocase; content:".ashx"; nocase; http.request_body; content:"__type"; nocase; content:"ObjectDataProvider"; nocase; fast_pattern; classtype:attempted-admin; reference:cve,CVE-2021-23758; reference:url,https://www.exploit.observer/?keyword=CVE-2021-23758&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=ajaxpro&match=exact; sid:1050602; rev:1;)

CVE-2021-23758.rules on GitHub

References

Exploits and technical analysis

https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/ (third-party-advisory)

Government sources

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758 (government-resource)

Other references

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.