GHSA-6r7c-6w96-8pvw CVE-2021-23758 SNYK-DOTNET-AJAXPRO2-1925971
Remote Code Execution in AjaxNetProfessional
- Severity
- 9.8 / 10
- Critical · CVSS 3.1
- Exploit chance (EPSS)
- 82.58%
- Chance of exploitation in the next 30 days. Higher than 99.67% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Aug 26, 2026
- Weakness
- CWE-502 Deserialization of Untrusted Data
- Fix
21.11.29.1- Upgrade AjaxNetProfessional to this version or later
Description
Overview
Affected versions of this package 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.
Description
Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating object from sequence of bytes is called deserialization. Serialization is commonly used for communication (sharing objects between multiple hosts) and persistence (store the object state in a file or a database). It is an integral part of popular protocols like Remote Method Invocation (RMI), Java Management Extension (JMX), Java Messaging System (JMS), Action Message Format (AMF), Java Server Faces (JSF) ViewState, etc.
Deserialization of untrusted data (CWE-502), is when the application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, letting the attacker to control the state or the flow of the execution.
Java deserialization issues have been known for years. However, interest in the issue intensified greatly in 2015, when classes that could be abused to achieve remote code execution were found in a popular library (Apache Commons Collection). These classes were used in zero-days affecting IBM WebSphere, Oracle WebLogic and many other products.
An attacker just needs to identify a piece of software that has both a vulnerable class on its path, and performs deserialization on untrusted data. Then all they need to do is send the payload into the deserializer, getting the command executed.
Developers put too much trust in Java Object Serialization. Some even de-serialize objects pre-authentication. When deserializing an Object in Java you typically cast it to an expected type, and therefore Java's strict type system will ensure you only get valid object trees. Unfortunately, by the time the type checking happens, platform code has already created and executed significant logic. So, before the final type is checked a lot of code is executed from the readObject() methods of various objects, all of which is out of the developer's control. By combining the readObject() methods of various classes which are available on the classpath of the vulnerable application an attacker can execute functions (including calling Runtime.exec() to execute local OS commands).
Releases
Releases before version 21.11.29.1 are affected. Please be careful to download any binary DLL from other web sites, especially we found NuGet packages not owned by us that contain vulnerable versions.
Workarounds
There is no workaround available that addresses all issues except updating to latest version from GitHub.
References
Find original CVE posting here: https://security.snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971
Note: the official Ajax.NET Professional (AjaxPro) NuGet package is available here: https://www.nuget.org/packages/AjaxNetProfessional/
For more information
If you have any questions or comments about this advisory:
- Open an issue on this GitHub repository
Affected versions
NuGet
| Package | Vulnerable | Fixed in |
|---|---|---|
| AjaxNetProfessional | <= 21.11.29 |
No fix yet |
| AjaxNetProfessional | < 21.11.29.1 |
21.11.29.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
AjaxNetProfessional NuGet → 21.11.29.1
- dotnet
dotnet add package AjaxNetProfessional --version 21.11.29.1
Severity breakdown
CVSS 3.1 9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-502: Deserialization of Untrusted Data
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
How to prevent it
- Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
- Implementation: When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
- Implementation: Explicitly define a final object() to prevent deserialization.
- Architecture and Design, Implementation: Make fields transient to protect them from deserialization. An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.
- Implementation: Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.
- Architecture and Design, Implementation: Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Added to CISA's Known Exploited Vulnerabilities catalog
- Last updated by the source
- Remediation due for U.S. federal agencies
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| CVE-2026-110879 jackson-databind validates the outer class of a class-name type ID but accepts attacker-selected classes inside its generic arguments, even when those classes… | Critical | Same weakness, CWE-502 |
| GHSA-6757-hggm-hp2w vLLM: Public multimodal SHM handle forgery reaches worker-side `pickle.loads()` with insecure serialization disabled | High | Same weakness, CWE-502 |
| GHSA-673q-mjm6-r5xr Next.js: Unauthenticated Remote Code Execution in `use cache` functions returning typed arrays | Critical | Same weakness, CWE-502 |
| GHSA-c27m-942f-rcfh Microsoft Security Advisory CVE-2026-87697 - .NET and Visual Studio Remote Code Execution Vulnerability | High | Same weakness, CWE-502 |
| GHSA-4w5f-7jp2-w48g Microsoft Security Advisory CVE-2026-83520 - .NET and Visual Studio Remote Code Execution Vulnerability | High | Same weakness, CWE-502 |
| GHSA-4j9v-h7pp-725h Microsoft Security Advisory CVE-2026-70035 - .NET and Visual Studio Remote Code Execution Vulnerability | High | Same weakness, CWE-502 |
| GHSA-gqvg-gmmx-x4hm MLFLOW_ALLOW_PICKLE_DESERIALIZATION=False safety control bypassed by mlflow.statsmodels flavor — RCE via crafted model artifact | High | Same weakness, CWE-502 |
| GHSA-gx83-3vf8-gh7j jackson-databind: Comparable missing from DefaultBaseTypeLimitingValidator's unsafe base types (incomplete PolymorphicTypeValidator denylist) | Medium | Same weakness, CWE-502 |
Credits: h0ng10, mwulftange
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