@hey-api/openapi-ts's buildClientParams template: prototype chain substitution via unknown $ ___proto__ key

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-48819: 0.27% estimated exploitation activity in the next 30 days; percentile 19.59 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary dist/clients/core/params.ts in @hey-api/openapi-ts ships a runtime template that is copied verbatim into every generated SDK as params.gen.ts. When a caller passes an object argument containing an unknown key starting with a slot prefix ($body, $headers, $path, $query), the function strips the prefix and writes the remainder directly to that slot without validation. The key "$queryproto" causes the returned params.query object to have its prototype chain substituted with attacker-controlled data. The issue is present in all versions through at least 0.97.2. Details The vulnerable branch in dist/clients/core/params.ts: This branch runs for any key that (1) is not registered in the field map and (2) starts with one of the four slot prefixes. When a caller passes "$queryproto" as an extra key alongside a legitimate field, the key is not in the field map, key.startsWith("$query") is true, and key.slice(7) produces "proto". The bracket-write params["query"]["proto"] = value…

Published by the source

1 Jul 2026, 20:55 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hhx9-57xq-r5rw

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-hhx9-57xq-r5rw

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# Patch Next advisory brief: CVE-2026-48819

Advisory: @hey-api/openapi-ts's `buildClientParams` template: prototype chain substitution via unknown `$ ___proto__` key
IDs: CVE-2026-48819, GHSA-hhx9-57xq-r5rw
Record: https://patchnext.com/advisories/cve-2026-48819 (revision 2, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @hey-api/openapi-ts 0.97.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @hey-api/openapi-ts: affected < 0.97.3; fixed in 0.97.3

## Suggested inspection (read-only)
- `npm ls @hey-api/openapi-ts --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @hey-api/openapi-ts.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-hhx9-57xq-r5rw (OSV record GHSA-hhx9-57xq-r5rw lists affected ranges: npm @hey-api/openapi-ts >=0 <0.97.3 (fixed))
- Verified: https://github.com/advisories/GHSA-hhx9-57xq-r5rw (GitHub-reviewed advisory GHSA-hhx9-57xq-r5rw lists affected ranges: npm @hey-api/openapi-ts >=0 <0.97.3)

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