The critical React2Shell unauthenticated remote code execution (RCE) vulnerability has been exploited to deploy Weaxor ransomware, S-RM reported Tuesday.

React2Shell, formally tracked as CVE-2025-55182, affects React Server Components versions 19.0.0, 19.1.0, 19.1.1 and 19.2.0, and has been under heavy exploitation since it was first disclosed on Dec. 3, 2025.

Most attacks thus far have been attributed to nation-state threat actors deploying backdoors and financially-motivated attackers deploying cryptominers.

In a new development, S-RM reports that it responded to an incident in which the maximum-severity vulnerability (CVSS 10.0) was used to gain initial access in a ransomware attack. The intrusion reportedly took place on Dec. 5, 2025, and was confined to the vulnerable web server with no additional lateral movement.

The attacker initially exploited React2Shell — which has multiple public proof-of-concept exploits available — by running a PowerShell command that led to the establishment of a Cobalt Strike beacon for command-and-control (C2) communication.

Once a C2 connection was established, and within less than a minute after initial access, the attacker deployed the Weaxor ransomware binary, which encrypts files and appends them with the file extension “.weax.”

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Impact

There is an unauthenticated remote code execution vulnerability in React Server Components.

We recommend upgrading immediately.

The vulnerability is present in versions 19.0.0, 19.1.0, 19.1.1, and 19.2.0 of: react-server-dom-webpack react-server-dom-parcel react-server-dom-turbopack

Patches

A fix was introduced in versions 19.0.1, 19.1.2, and 19.2.1. If you are using any of the above packages please upgrade to any of the fixed versions immediately.

If your app’s React code does not use a server, your app is not affected by this vulnerability. If your app does not use a framework, bundler, or bundler plugin that supports React Server Components, your app is not affected by this vulnerability.

References

See the blog post for more information and upgrade instructions.