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Builder.io Gen2 SDKs EUVDEUVD-2026-81044

| CVE-2026-92781 MEDIUM
Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution) (CWE-1321)
2026-09-16 VulnCheck GHSA-mgr8-fxxv-82mj
Information Disclosure Prototype Pollution JavaScript Builder Io Sdk React Builder Io Sdk Vue Builder Io Sdk Svelte Builder Io Sdk Solid Builder Io Sdk Qwik Builder Io Sdk Angular Builder Io Sdk React Nextjs
5.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
5.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
6.3 MEDIUM

Remote unauthenticated crafted link but victim must open it (UI:R); client-side prototype pollution yields low, gadget-dependent C/I/A impact with no scope change.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

2
Metadata Corrected
Sep 16, 2026 - 22:40 vuln.today
tag: JavaScript added
Analysis Generated
Sep 16, 2026 - 22:17 vuln.today

DescriptionCVE.org

Builder.io Gen2 SDKs through versions 5.2.11 and 0.25.13 contain a prototype pollution vulnerability in the unflatten helper that processes builder.userAttributes query parameters without prototype guards. Attackers can craft preview links with __proto__ or prototype segments to pollute Object.prototype in a visitor's browser when the SDK processes the malicious URL.

AnalysisAI

Prototype pollution in the unflatten helper of Builder.io Gen2 SDKs (the @builder.io/sdk-react, sdk-vue, sdk-svelte and sdk-solid packages at or below 5.2.11, and sdk-angular, sdk-react-nextjs and sdk-qwik at or below 0.25.13) lets unauthenticated remote attackers poison Object.prototype in a victim's browser by luring the victim into opening a crafted preview link whose builder.userAttributes query parameters carry __proto__ or prototype segments. Exploitation is not automatable against a passive server - it hinges on user interaction (UI:P), because the SDK must actually be running in the victim's browser when the malicious URL is processed, and real harm (DOM XSS, client-side logic tampering, denial of service) only materializes if downstream application code reads the polluted inherited properties. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Requires the SDK to process a client-supplied URL carrying builder.userAttributes query parameters - this is the preview/personalization code path in Builder.io Gen2 SDKs at or below 5.2.11 (svelte/vue/react/solid) and 0.25.13 (angular/react-nextjs/qwik). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Moderate-to-low real-world risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade every affected package past its vulnerable ceiling - @builder.io/sdk-react, sdk-vue, sdk-svelte and sdk-solid above 5.2.11, and sdk-angular, sdk-react-nextjs and sdk-qwik above 0.25.13 - while noting that an exact patched release number is not independently confirmed from the available data, so confirm the fixed build against the vendor repository https://github.com/BuilderIO/builder, the tracking issue https://github.com/BuilderIO/builder/issues/4824 and the VulnCheck advisory https://www.vulncheck.com/advisories/builder-io-gen2-sdks-through-5.2.11-prototype-pollution-via-builder-userattributes before pinning. … Detailed patch versions, workarounds, and compensating controls in full report.
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Same weakness CWE-1321 – Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

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Same technique Information Disclosure

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EUVD-2026-81044 vulnerability details – vuln.today
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