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ExploitedIn CISA KEVFix available

CVE-2021-23758

Exploitation confirmed. First attested on 2026-08-26 by CISA-ADP, CISA KEV, GCVE · previdian.

  • Published2021-12-03
  • WeaknessCWE-502

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-12-0320:15CVE publishedNVD
  2. 2026-08-26Added to the CISA KEV catalogCISA KEV
  3. 2026-08-26Listed as exploited by GCVEGCVE
  4. 2026-08-26Exploitation first reportedCISA KEV
  5. 2026-08-2617:44SSVC exploitation set to activeCISA-ADP

Observed activity

isMalicious corpus · updated 2026-11-04 03:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-23758?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-23758?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Ajaxpro.2 project ajaxpro.2
BranchAffectedFixed in
—all versionsno fix published
Michaelschwarz ajax.net professional
BranchAffectedFixed in
21.10< 21.10.30.121.10.30.1
AjaxNetProfessional
BranchAffectedFixed in
21.11< 21.11.29.121.11.29.1

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As snyk, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • AjaxPro.2
    Affected
    • = 0no fix statedcustom

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2023-11-14

Fix

  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 evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.due 2026-09-09

Advisories and patches

Detection

read 2026-11-03 22:42 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiednumanturle/CVE-2021-23758-POC
PoC-in-GitHub
Metasploit modules
1 moduleexploit/windows/http/ajaxpro_deserialization_rcerank: excellentModule metadata: Metasploit Framework, © Rapid7, Inc., BSD-3-Clause.
Metasploit Framework

CISA Known Exploited Vulnerability

Date Added
2026-08-26
Patch Due Date
2026-09-09
Ransomware Use
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.

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-12-03
Last Modified
2026-08-27
NVD status
Analyzed
GitHub Advisory
GHSA-6r7c-6w96-8pvw GHSA-74r6-grj9-8rq6

Frequently asked questions

What is CVE-2021-23758?

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.

Is CVE-2021-23758 actively exploited?

Yes. CVE-2021-23758 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, meaning it has been confirmed as actively exploited in the wild. CISA requires federal agencies to patch by 2026-09-09.

What is the CVSS score for CVE-2021-23758?

CVE-2021-23758 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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