CVE-2026-48819Hey API: `buildClientParams` template: prototype chain substitution via unknown `$<slot>___proto__` key
- 4.8MediumCVSS base score
- 0.27%Exploitation in 30 daysEPSS · top 80% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- YesPublic exploitsa reference or SSVC says so
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.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. A reference of the record is tagged as an exploit. CISA's SSVC rates its exploitation: a proof of concept is public.
Show the exploits1
References tagged exploit1 reference
- https://github.com/hey-api/hey-api/security/advisories/GHSA-hhx9-57xq-r5rw (opens in a new tab)x_refsource_CONFIRMexploit
Timeline
ID reserved
By GitHub_M
- 56 days later
· 56 days later
Published
- 3 days later
· 3 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium4.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N |
| NVDNVD · Deferred | 3.1 | Medium4.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.27% · top 80% of all CVEs (14 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 4.8.
Affected products
- affected < 0.97.3
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- npm@hey-api/openapi-tsGHSA-hhx9-57xq-r5rw (opens in a new tab)
References
References4
- https://github.com/hey-api/hey-api/security/advisories/GHSA-hhx9-57xq-r5rw (opens in a new tab)x_refsource_CONFIRMexploit
- https://github.com/hey-api/hey-api/commit/023909137a15eff9c0263d3bcd116140076b214f (opens in a new tab)x_refsource_MISC
- https://github.com/hey-api/hey-api/commit/da321a1529eb3c90d2109da870f514b915a60169 (opens in a new tab)x_refsource_MISC
- https://github.com/hey-api/hey-api/releases/tag/%40hey-api%2Fopenapi-ts%400.97.3 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-45267 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-hhx9-57xq-r5rw (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-48819)Record last updated .