Prototype pollution via unchecked array index lookup
Published Mar 20, 2026 · Updated Mar 20, 2026
Prototype pollution in WebReflection flatted before 3.4.2 allows attackers to expose Array.prototype through crafted JSON. The resolver in esm/index.js and cjs/index.js uses attacker-controlled parsed strings as array keys, so proto resolves through the inherited getter and is assigned to the returned object. Exploitation requires downstream code to write through that returned reference, which then pollutes the global array prototype and can cause service interruption or code execution.
Summary
What happened
Prototype pollution in WebReflection flatted before 3.4.2 allows attackers to expose Array.prototype through crafted JSON. The resolver in esm/index.js and cjs/index.js uses attacker-controlled parsed strings as array keys, so proto resolves through the inherited getter and is assigned to the returned object. Exploitation requires downstream code to write through that returned reference, which then pollutes the global array prototype and can cause service interruption or code execution.
The record
- CVE
- CVE-2026-33228
- Published
- Mar 20, 2026
- Updated
- Mar 20, 2026
- Vendor
- WebReflection
- Product
- flatted
- Classifications
- CWE-1321
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 20, 2026CVE publishedPublication date reported by the CVE source.
- Mar 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 3.4.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
- GHSA-rf6f-7fwh-wjgh replication stepsproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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