Prototype Pollution via FormData Processing in Qwik City

Exploitation

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

CVSS

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

EPSS

• CVE-2026-25150: 0.72% estimated exploitation activity in the next 30 days; percentile 53.93 (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 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.

Published by the source

3 Feb 2026, 20:49 UTC

Last modified by the source

4 Feb 2026, 18:09 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-xqg6-98cw-gxhq

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-xqg6-98cw-gxhq

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-xqg6-98cw-gxhq

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# Patch Next advisory brief: CVE-2026-25150

Advisory: Prototype Pollution via FormData Processing in Qwik City
IDs: CVE-2026-25150, GHSA-xqg6-98cw-gxhq
Record: https://patchnext.com/advisories/cve-2026-25150 (revision 3, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @builder.io/qwik-city 1.19.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @builder.io/qwik-city: affected < 1.19.0; fixed in 1.19.0

## Suggested inspection (read-only)
- `npm ls @builder.io/qwik-city --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 @builder.io/qwik-city.
- 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://github.com/advisories/GHSA-xqg6-98cw-gxhq (GitHub-reviewed advisory GHSA-xqg6-98cw-gxhq lists affected ranges: npm @builder.io/qwik-city >=0 <1.19.0)
- Verified: https://osv.dev/vulnerability/GHSA-xqg6-98cw-gxhq (OSV record GHSA-xqg6-98cw-gxhq lists affected ranges: npm @builder.io/qwik-city >=0 <1.19.0 (fixed))

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