CVE-2021-43853: Ajax.NET Professional (AjaxPro) is an AJAX framework available for Microsoft ASP.NET

Q: How do I fix CVE-2021-43853?

ajax.net professional: upgrade to 21.12.22.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-43853 being exploited?

CVE-2021-43853 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-43853 affect?

CVE-2021-43853 affects ajax.net professional. Severity is high (CVSS 8.7). Ajax.NET Professional (AjaxPro) is an AJAX framework available for Microsoft ASP.NET. Affected versions of this package are vulnerable to JavaScript object injection which may result in cross site scripting when leveraged by a malicious use

Q: How urgent is CVE-2021-43853?

Priority 50/100. High severity; On your watchlist

This month

HIGH 8.7WATCHLISTUPGRADE

CVE-2021-43853 is a high-severity flaw (CVSS 8.7) affecting ajax.net professional. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Ajax.NET Professional (AjaxPro) is an AJAX framework available for Microsoft ASP.NET. Affected versions of this package are vulnerable to JavaScript object injection which may result in cross site scripting when leveraged by a malicious user. The affected core relates to JavaScript object creation when parsing json input. Releases before version 21.12.22.1 are affected. A workaround exists that replaces one of the core JavaScript files embedded i

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.7 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.9% (top 42%)
CISA exploited list	No
Weakness	CWE-79, CWE-502
Published	2021-12-22
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: ajax.net professional project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-12-22 21:15 UTCPublished CVE record published
2026-06-17 04:11 UTCUpdated Record last modified

ajax.net professional project ajax.net professional UPGRADE

Affected: < 21.12.22.1

Fixed in: 21.12.22.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ajax.net-professional || rpm -q ajax.net-professional || ajax.net-professional --version

2. UPGRADE to 21.12.22.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ajax.net-professional

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ajax.net-professional

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-43853?

ajax.net professional: upgrade to 21.12.22.1. Exact commands for each OS are on this page.

Is CVE-2021-43853 being exploited?

CVE-2021-43853 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-43853 affect?

CVE-2021-43853 affects ajax.net professional. Severity is high (CVSS 8.7). Ajax.NET Professional (AjaxPro) is an AJAX framework available for Microsoft ASP.NET. Affected versions of this package are vulnerable to JavaScript object injection which may result in cross site scripting when leveraged by a malicious use

How urgent is CVE-2021-43853?

Priority 50/100. High severity; On your watchlist

Software pages

.NET vulnerabilities

Related CVEs

CVE-2021-23758 HIGH 8.1 EXPLOITED MITIGATE UPGRADE Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
CVE-2023-49289 MEDIUM 6.3 UPGRADE Ajax.NET Professional (AjaxPro) is an AJAX framework for Microsoft ASP.NET which will create proxy JavaScript

References

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