CVE-2026-28794: `@orpc/client` has Prototype Pollution via `StandardRPCJsonSerializer` Deserialization

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 1.3%, percentile 69: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 69% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes @orpc/client (npm) <= 1.13.5, fixed in 1.13.6. Check your lockfile, including transitive dependencies.

What it is

oRPC is an tool that helps build APIs that are end-to-end type-safe and adhere to OpenAPI standards. Prior to version 1.13.6, a 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. This issue has been patched in version 1.13.6.

From the GitHub advisory

Summary 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:

https://github.com/middleapi/orpc/blob/819ed2e0897b18a5d6a4ca85ba68568f055004a1/packages/client/src/adapters/standard/rpc-json-serializer.ts#L137-L213

There are two primary distinct write vectors available to an attacker:

1. The meta vector: Writes type-constrained values (e.g., Map, Set, Date) to arbitrary object paths. 2. The maps vector: Allows the injection of arbitrary string values. This occurs because the return value of getBlob(i) (which relies on FormData.get(i.toString())) is cast as Blob. Since this is strictly a TypeScript compile-time cast, the runtime execution allows standard text fields to return as arbitrary strings.

Weakness type: CWE-1321.

Product: @orpc/client (npm) · Assigned by: GitHub_M · Published: 2026-03-06

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.25% probability of exploitation activity in the next 30 days; percentile 69.

Timeline

• 2026-03-02 — GitHub-reviewed advisory GHSA-m272-9rp6-32mc published (critical)
• 2026-03-06 — CVE record published by GitHub_M
• 2026-03-09 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-m272-9rp6-32mc github.com
2. CVE.org record CVE-2026-28794 cve.org
3. NVD entry CVE-2026-28794 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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