Prototype Pollution via FormData Processing in Qwik City
Summary
A Prototype Pollution vulnerability exists in the formToObj() function within @builder.io/qwik-city middleware. The function processes form field names with dot notation (e.g., user.name) to create nested objects, but fails to sanitize dangerous property names like __proto__, constructor, and prototype. This allows unauthenticated attackers to pollute Object.prototype by sending crafted HTTP POST requests, potentially leading to privilege escalation, authentication bypass, or denial of service.
Impact
An unauthenticated attacker can supply specially crafted form field names that cause formToObj() to write dangerous keys (for example proto, constructor, prototype) into parsed objects. This results in Prototype Pollution of the server process and can cause privilege escalation, auth bypass, denial-of-service, or other global application integrity failures depending on how objects are used.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @builder.io/qwik-city | < 1.19.0 | 1.19.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:L- Weakness (CWE)
CWE-1321- Platform
- npm
- Package
@builder.io/qwik-city- Disclosed
- 03.02.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-xqg6-98cw-gxhq - CC BY 4.0
Vulnerability history: @builder.io/qwik-city
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 8
- First → latest
- 04.2023 03.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 1
- Medium 4
- Low 1
Disclosures per year
- 2023: 1
- 2024: 0
- 2025: 1
- 2026: 6
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Prototype Pollution via FormData Processing in Qwik City this entry
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