CVE-2021-43853Network attack vector

Cross-site scripting via eval-based JSON parsing

Published Dec 22, 2021 · Updated Aug 4, 2024

Cross-site scripting in Ajax.NET Professional before 21.12.22.1 allows remote authenticated users to execute script via crafted JSON. AjaxPro/core.js rewrites recognized date tokens and then passes the entire response text to eval without rejecting other JavaScript expressions. Exploitation requires an affected ASP.NET integration and victim interaction, after which script runs in the victim's browser context.

CVSS severity8.7
High
EPSS probability0.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Ajax.NET Professional before 21.12.22.1 allows remote authenticated users to execute script via crafted JSON. AjaxPro/core.js rewrites recognized date tokens and then passes the entire response text to eval without rejecting other JavaScript expressions. Exploitation requires an affected ASP.NET integration and victim interaction, after which script runs in the victim's browser context.

The record

CVE
CVE-2021-43853
Published
Dec 22, 2021
Updated
Aug 4, 2024
Vendor
Michael Schwarz
Product
Ajax.NET Professional
Classifications
CWE-502, CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 21.12.22.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Michael Schwarz · Ajax.NET Professionalversion=< 21.12.22.1

Published CVSS scores

8.7GitHubCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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