CVE-2026-25150: Prototype Pollution via FormData Processing in Qwik City

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 53: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 53% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes @builder.io/qwik-city (npm) < 1.19.0, fixed in 1.19.0. Check your lockfile, including transitive dependencies.

What it is

Qwik is a performance focused javascript framework. Prior to version 1.19.0, 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. This issue has been patched in version 1.19.0.

From the GitHub advisory

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.

Weakness type: CWE-1321.

Product: @builder.io/qwik-city (npm) · Assigned by: GitHub_M · Published: 2026-02-03

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.72% probability of exploitation activity in the next 30 days; percentile 53.

Timeline

• 2026-02-03 — CVE record published by GitHub_M
• 2026-02-03 — GitHub-reviewed advisory GHSA-xqg6-98cw-gxhq published (critical)
• 2026-02-04 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-xqg6-98cw-gxhq github.com
2. CVE.org record CVE-2026-25150 cve.org
3. NVD entry CVE-2026-25150 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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