How severe is CVE-2021-23758?

CVE-2021-23758 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-23758?

CVE-2021-23758 affects the following packages: AjaxNetProfessional (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2021-23758?

Update AjaxNetProfessional to 21.11.29.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23758 is resolved across your whole dependency graph.

How do I detect CVE-2021-23758 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for AjaxNetProfessional. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2021-23758 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-23758?

O3 pinpoints whether CVE-2021-23758 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-23758 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-23758, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

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

CVE-2021-23758 has an EPSS (Exploit Prediction Scoring System) score of 88.8%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-23758?

CVE-2021-23758 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-23758 published, and has it been updated?

CVE-2021-23758 was published on December 3, 2021 and was last updated on March 13, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET NuGet

CVE-2021-23758

CRITICAL

Remote Code Execution in AjaxNetProfessional

Also known asGHSA-6r7c-6w96-8pvw

Published

Dec 3, 2021

Updated

Mar 13, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

88.8%probability of exploitation in next 30 days

Very High Risk100th percentile+0.99%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

.NETAjaxNetProfessional

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`AjaxNetProfessional`	all versions	21.11.29.1

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

All versions of package ajaxpro.2 are vulnerable to Deserialization of U…

github.comGithubDec 2021

All versions of package ajaxpro.2 are vulnerable to Deserialization of U…

github.comMetasploitNov 2023

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for AjaxNetProfessional. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update AjaxNetProfessional to 21.11.29.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23758 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-23758 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2021-23758. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-23758 in your dependencies?

O3 detects CVE-2021-23758 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works