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Vulnerability · Published Jul 17, 2026 · Assigned by GitHub_M

CVE-2026-48819Hey API: `buildClientParams` template: prototype chain substitution via unknown `$<slot>___proto__` key

Medium 4.8

In plain English

A medium-severity prototype pollution in openapi-ts from hey-api. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.8Medium
Exploit odds (30 days)0.3%top 80.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

Hey API is an ecosystem for turning API specifications into production-ready code. Prior to 0.97.3, dist/clients/core/params.ts ships a runtime template copied into generated SDKs as params.gen.ts, and buildClientParams writes unknown slot-prefixed keys such as $body_, $headers_, $path_, and $query_ directly to the corresponding slot, allowing $query___proto__ alongside a legitimate q field to set params.query through params["query"]["__proto__"] = value, call Object.setPrototypeOf(params.query, value), and expose inherited attacker-controlled keys during for..in iteration. This issue is fixed in version 0.97.3.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npm@hey-api/openapi-ts0.97.3GHSA-hhx9-57xq-r5rw

Affected products (as reported)

VendorProductVersions
hey-api openapi-ts < 0.97.3

Weakness: CWE-1321 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

References