CVE-2026-6621
Raw vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P/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:XSummary
CVE-2026-6621 is a medium-severity Code Injection (CWE-94) vulnerability. Its CVSS base score is 6.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked at the 26th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-6621 affects the 1024bit extend-deep package up to version 0.1.6, specifically an unknown function in the index.js file. The vulnerability involves manipulation of the __proto__ argument, resulting in improperly controlled modification of object prototype attributes. It is classified under CWE-94 (code injection) and CWE-1321 (prototype pollution), with a CVSS v3.1 base score of 7.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L). The issue was published on 2026-04-20.
Remote exploitation is possible without authentication or user interaction, allowing unauthenticated attackers accessible over the network to trigger the prototype pollution. Successful exploitation can lead to low impacts on confidentiality, integrity, and availability through modification of object prototypes.
Advisories referenced in VulDB entries (vuldb.com/vuln/358256 and related pages) document the issue, while a GitHub security research repository provides a proof-of-concept (PoC.md) demonstrating the prototype pollution. The project's code repository has not been active for many years, indicating no official patches or updates are available.
The exploit has been publicly disclosed and may be utilized by attackers.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-23812
Vulnerability Data
A vulnerability was determined in 1024bit extend-deep up to 0.1.6. The impacted element is an unknown function of the file index.js. This manipulation of the argument __proto__ causes improperly controlled modification of object prototype attributes. Remote exploitation of the attack…
more
is possible. The exploit has been publicly disclosed and may be utilized. The code repository of the project has not been active for many years.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V15.3.6V1.3.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation finds code paths that accept and execute externally influenced strings.
Input validation directly stops untrusted data from being used to construct executable code without neutralization.
Least privilege limits the damage an injected code fragment can perform once executed.
Requiring documented secure development standards and tools enforces use of safe code-generation APIs and escaping.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
PR.PS-06's SDLC practices directly target injection flaws via secure coding and testing (mostly), yet as a single broad outcome it leaves many code-generation specifics unaddressed (partial).
PR.DS-10 protects runtime data confidentiality/integrity but has no bearing on neutralizing externally influenced input during code generation, so neither direction shows any preventive effect.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development catches prototype-pollution flaws before release.
Secure development lifecycle mandates input validation and object-handling controls that directly prevent prototype pollution.
Application security requirements explicitly call for safeguards against unsafe object attribute manipulation.
Secure architecture principles reduce the likelihood of prototype pollution through safe design patterns.
Banning unapproved code samples and unauthenticated web services, combined with secure-coding standards and SAST, prevents the dynamic generation or inclusion of attacker-supplied code.
Change-management processes ensure security fixes for prototype-pollution issues are tracked and deployed.