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Known exploited vulnerability

CVE-2021-23758

criticalCVSS 3.1 9.8In CISA KEVEPSS 83%Published · n/a

The short answer

CVE-2021-23758 affects n/a AjaxPro.2 and is rated critical (CVSS 9.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-26: attackers are using it, so patch it first. Fixed versions are published for AjaxNetProfessional (21.11.29.1).

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.

Weakness: CWE-502.

Severity

9.8 critical

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploited (CISA KEV)

Yes, since Aug 26, 2026

Federal due date Sep 9, 2026

EPSS, next 30 days

83%

Higher than 100% of scored CVEs

How it can be exploited

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

What CISA says to do

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…

Affected packages and fixed versions

PackageEcosystemFixed inAdvisory
AjaxNetProfessionalNuGet21.11.29.1GHSA-6r7c-6w96-8pvw

Is it in your code? Drop your lockfile into the free vulnerability check, or let vulnerability watch check your repository every day and open the upgrade as a pull request.

Affected products

AjaxPro.2. NVD's record lists the exact affected versions.

References

Questions

Is CVE-2021-23758 being exploited?

Yes. CISA added CVE-2021-23758 to its Known Exploited Vulnerabilities catalog on 2026-08-26, with a federal remediation due date of 2026-09-09.

How do I fix CVE-2021-23758?

Upgrade to a fixed version: AjaxNetProfessional (NuGet) 21.11.29.1. CISA's 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…

From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.

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