CVE-2026-92779 Overview
Builder.io Gen2 SDKs through versions 5.2.11 and 0.25.13 contain a prototype pollution vulnerability [CWE-1321] in the deep-set helper function. The function processes content block bindings without validating dangerous property keys. Attackers craft content blocks with binding keys containing __proto__, prototype, or constructor paths. During rendering, these keys pollute Object.prototype and affect all subsequent objects created in the process. In multi-tenant deployments, the pollution persists across other tenants' renders within the same runtime.
Critical Impact
Attackers can manipulate application logic, escalate privileges, or inject controlled properties into unrelated tenant renders sharing the same Node.js process.
Affected Products
- Builder.io Gen2 SDK versions through 5.2.11
- Builder.io Gen2 SDK versions through 0.25.13
- Applications embedding vulnerable SDK versions in server-side rendering pipelines
Discovery Timeline
- 2026-09-16 - CVE-2026-92779 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-92779
Vulnerability Analysis
The vulnerability resides in the deep-set helper used by the SDK's get-processed-block logic. Builder.io content blocks expose a bindings object whose keys represent property paths written into a target object. The SDK walks each path segment and assigns nested properties without filtering reserved JavaScript identifiers. Supplying a binding key such as __proto__.polluted writes directly to the base prototype chain rather than a scoped instance.
Because Object.prototype is shared across every object in a JavaScript runtime, the injected property propagates to unrelated objects. In server-side rendering environments handling multiple tenants, one attacker-controlled content block contaminates all subsequent renders in the same process. The consequences depend on downstream code paths that read the polluted property, ranging from authorization bypass to logic manipulation.
Root Cause
The root cause is missing validation of user-controlled property paths in the set function. The implementation iterates path segments and creates or overwrites properties without checking against a deny list of __proto__, prototype, and constructor. Content bindings originate from untrusted Builder.io content data that may be modified through the CMS or intercepted API calls.
Attack Vector
An attacker with permission to author or modify Builder.io content blocks submits a block containing crafted binding keys. When any SDK consumer renders that block, the deep-set operation pollutes Object.prototype. Exploitation requires low privileges to author content and no user interaction. The referenced source lines in packages/sdks/src/functions/get-processed-block.ts and packages/sdks/src/functions/set.ts document the vulnerable assignment flow. See the VulnCheck Advisory for Builder.io and GitHub Issue #4823 for additional technical context.
Detection Methods for CVE-2026-92779
Indicators of Compromise
- Builder.io content blocks containing binding keys with substrings __proto__, prototype, or constructor
- Unexpected properties appearing on plain objects during server-side rendering telemetry
- Cross-tenant data leakage or authorization anomalies in multi-tenant SSR services
- SDK log entries showing unusual deep property assignments during block processing
Detection Strategies
- Inspect stored Builder.io content payloads for dangerous keys in the bindings map before rendering
- Instrument the set helper to log or reject paths containing reserved prototype identifiers
- Add runtime assertions that verify Object.prototype remains free of unexpected enumerable properties between requests
Monitoring Recommendations
- Enable audit logging for content block create and update operations in the Builder.io CMS
- Monitor Node.js process metrics for behavioral changes following content deployments
- Correlate SSR error rates with recent content publishing events to surface exploitation attempts
How to Mitigate CVE-2026-92779
Immediate Actions Required
- Upgrade Builder.io Gen2 SDKs to a fixed release beyond 5.2.11 and 0.25.13 as published by the maintainers
- Audit existing content blocks for binding keys containing __proto__, prototype, or constructor and remove them
- Restrict content authoring privileges to trusted users until patches are applied
- Recycle server-side rendering processes after remediation to clear any residual pollution
Patch Information
Refer to the Builder.io GitHub Repository and GitHub Issue #4823 for patch status and release notes. Review the vulnerable code paths in the get-processed-block source and the set function source.
Workarounds
- Wrap the SDK set function to reject any path segment matching __proto__, prototype, or constructor
- Sanitize Builder.io content responses at the application layer before invoking render functions
- Use Object.create(null) for target objects passed to deep-set operations where feasible
- Freeze Object.prototype at process startup with Object.freeze(Object.prototype) to block prototype writes
# Configuration example
# Node.js startup flag to harden the runtime against prototype pollution
node --disable-proto=delete server.js
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.