Summary
@orpc/client has Prototype Pollution via StandardRPCJsonSerializer Deserialization
A critical Prototype Pollution vulnerability exists in the RPC JSON deserializer of the @orpc/client package. The vulnerability allows unauthenticated, remote attackers to inject arbitrary properties into the global Object.prototype. Because this pollution persists for the lifetime of the Node.js process and affects all objects, it can lead to severe security breaches, including authentication bypass, denial of service, and potentially Remote Code Execution.
Vulnerability Details
The root cause lies in the deserialize() method of StandardRPCJsonSerializer. When processing attacker-controlled path segments from the meta and maps arrays, the deserializer fails to implement validation or sanitization for dangerous JavaScript object keys, specifically __proto__ and constructor:
There are two primary distinct write vectors available to an attacker:
- The
metavector: Writes type-constrained values (e.g.,Map,Set,Date) to arbitrary object paths. - The
mapsvector: Allows the injection of arbitrary string values. This occurs because the return value ofgetBlob(i)(which relies onFormData.get(i.toString())) is castas Blob. Since this is strictly a TypeScript compile-time cast, the runtime execution allows standard text fields to return as arbitrary strings.
Crucially, this deserialization process occurs at the very beginning of the request lifecycle before any Zod schema validation takes place. Consequently, a malicious payload will successfully pollute the prototype even if the request is subsequently rejected by the validation layer.
This issue impacts all server adapters utilizing the RPC protocol.
Proof of Concept
To reproduce the vulnerability, set up the playgrounds/astro environment and start the development server using pnpm dev.
Run the following curl command to send a crafted payload:
curl -X POST http://localhost:4321/rpc/planet/create \
-F 'data={"json":{},"meta":[],"maps":[["__proto__","role"]]}' \
-F '0=admin'
Result: The deserializer evaluates maps, follows the __proto__ path, and maps index 0 to the string "admin". This immediately applies Object.prototype.role = "admin" across the entire Node.js server instance.
Impact
Servers relying on StandardRPCJsonSerializer for deserialization are immediately susceptible to global prototype pollution. The potential impacts including:
- Privilege Escalation / Authorization Bypass: Attackers can bypass flawed security checks. For example, if the server relies on a defaulted property check like
if (user.role === "admin"), the application will evaluate this astruefor all users globally. - Remote Code Execution: If the application or its dependencies contain susceptible prototype pollution gadgets (e.g., dynamically executing shell commands or scripts based on object properties), this vulnerability can be leveraged into full RCE.
- Denial of Service: Attackers can overwrite built-in methods (e.g.,
toString) or set objects into unexpected states, causing the application to crash or throw unhandled exceptions globally.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-28794? CVE-2026-28794 is a critical-severity security vulnerability in @orpc/client (npm), affecting versions <= 1.13.5. It is fixed in 1.13.6.
- Which versions of @orpc/client are affected by CVE-2026-28794? @orpc/client (npm) versions <= 1.13.5 is affected.
- Is there a fix for CVE-2026-28794? Yes. CVE-2026-28794 is fixed in 1.13.6. Upgrade to this version or later.
- Is CVE-2026-28794 exploitable, and should I be worried? Whether CVE-2026-28794 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-28794 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-28794? Upgrade
@orpc/clientto 1.13.6 or later.