Prototype pollution via flat custom-message error codes
Published Sep 13, 2026 · Updated Sep 13, 2026
Prototype pollution in joi before 17.13.8 and 18.2.9 allows attackers to replace an object's prototype through custom messages. The messages compilation function accepts proto as a flat error-code key and assigns through it, replacing the prototype of the returned messages object. Exploitation requires an application to pass attacker-controlled keys into custom-message configuration; affected downstream code can lose expected Object.prototype methods or follow attacker-influenced property lookups.
Summary
What happened
Prototype pollution in joi before 17.13.8 and 18.2.9 allows attackers to replace an object's prototype through custom messages. The messages compilation function accepts proto as a flat error-code key and assigns through it, replacing the prototype of the returned messages object. Exploitation requires an application to pass attacker-controlled keys into custom-message configuration; affected downstream code can lose expected Object.prototype methods or follow attacker-influenced property lookups.
The record
- CVE
- CVE-2026-90771
- Published
- Sep 13, 2026
- Updated
- Sep 13, 2026
- Vendor
- hapi.js
- Product
- joi
- Classifications
- Unavailable
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 13, 2026CVE publishedPublication date reported by the CVE source.
- Sep 13, 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=16.0.0 <17.13.8
- Affected versionversion=18.0.0 <18.2.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
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Public exploit references
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Technologies
Your stack
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Your stack
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