Prototype pollution via unchecked __proto__ merge
Published Apr 20, 2026 · Updated Apr 20, 2026
Prototype pollution in 1024bit extend-deep 0.1.6 and earlier allows remote attackers to alter inherited object properties via crafted input. The recursive merge loop in index.js enumerates source keys and descends into target[k] without rejecting proto, causing a parsed object to rewrite Object.prototype. Exploitation requires an application to pass attacker-controlled objects to the library; the demonstrated consequence is property injection across existing and future objects.
Summary
What happened
Prototype pollution in 1024bit extend-deep 0.1.6 and earlier allows remote attackers to alter inherited object properties via crafted input. The recursive merge loop in index.js enumerates source keys and descends into target[k] without rejecting proto, causing a parsed object to rewrite Object.prototype. Exploitation requires an application to pass attacker-controlled objects to the library; the demonstrated consequence is property injection across existing and future objects.
The record
- CVE
- CVE-2026-6621
- Published
- Apr 20, 2026
- Updated
- Apr 20, 2026
- Vendor
- 1024bit
- Product
- extend-deep
- Classifications
- CWE-94, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 20, 2026CVE publishedPublication date reported by the CVE source.
- Apr 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0.1.0
- Affected versionversion=0.1.1
- Affected versionversion=0.1.2
- Affected versionversion=0.1.3
- Affected versionversion=0.1.4
- Affected versionversion=0.1.5
- Affected versionversion=0.1.6
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
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- extend-deep prototype-pollution proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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