CVE-2026-27971: Qwik Unauthenticated RCE via server$ Deserialization Vulnerability
Summary
CVE-2026-27971: Qwik vulnerable to Unauthenticated RCE via server$ Deserialization. Affects @builder.io/qwik versions < 1.19.1. Fixed in 1.19.1. How to fix ↓
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Background
Qwik is a modern framework for building fast and efficient web applications. It allows developers to create applications that are highly optimized for performance and user experience. However, versions of Qwik up to 1.19.0 have a critical vulnerability that exposes applications to remote code execution (RCE) due to unsafe deserialization in the server$ RPC mechanism.
Vulnerability Detail
The vulnerability arises from the server$ RPC mechanism in Qwik, which allows for unsafe deserialization of data. This flaw enables any unauthenticated user to send a specially crafted HTTP request that can execute arbitrary code on the server. The impact of this vulnerability is severe, as it can lead to complete server compromise, data breaches, and unauthorized access to sensitive information. The vulnerability is particularly dangerous in environments where the 'require()' function is available at runtime, allowing for the execution of malicious code.
How To Fix
Latest published version: 1.20.2 as of 23 Oct 2026
npm install @builder.io/qwik@1.20.2Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
1.19.1
This is the first release that contains the fix.
npm install @builder.io/qwik@1.19.1Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you can restrict access to the server$ RPC mechanism to authenticated users only. This can be done by implementing proper authentication checks before allowing access to the RPC endpoints. However, this is not a permanent solution, and updating to the patched version is strongly recommended.
Conclusion
The Qwik framework has a critical vulnerability (CVE-2026-27971) that allows unauthenticated remote code execution due to unsafe deserialization. It is crucial to update to version 1.19.1 or later to mitigate this risk. Implementing temporary workarounds can help, but they are not substitutes for applying the patch.
See every vulnerability recorded for @builder.io/qwik →
FAQ
The CVSS score of this vulnerability is 9.2, indicating a critical level of severity.
You can use Vulert to monitor and alert for open-source vulnerabilities in your software. Without requiring access to the code or installation, Vulert uses just package-lock.json to check for vulnerabilities. You can also use the Vulert playground at Vulert Scanner to check your application.
The potential consequences include remote code execution, unauthorized access to sensitive data, and complete server compromise.
While the best solution is to update to the patched version, you can mitigate the risk by restricting access to the vulnerable RPC mechanism to authenticated users only.
If you cannot update the package immediately, implement strict authentication checks for the server$ RPC mechanism to minimize the risk of exploitation.
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