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

> Remote attackers can achieve code execution or privilege escalation via prototype pollution in the extend-deep library, which lacks active maintenance.

- **Severity:** Medium 6.9 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-vr46-pfqh-wpf8

## What is CVE-2026-6621?

CVE-2026-6621 is a medium-severity code injection vulnerability in 1024bit extend-deep, published on 20 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-94 (Improper Control of Generation of Code), CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-6621?


## How do I fix CVE-2026-6621?

No fix has been published for CVE-2026-6621 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6621 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6621 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6621 and fix it if it is affected.

What it is: CVE-2026-6621 is a medium-severity code injection vulnerability in 1024bit extend-deep, published on 20 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6621 exists.

Affected product: 1024bit extend-deep. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-6621/ (Markdown: https://insights.sbomify.com/CVE-2026-6621/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6621
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6621
- OSV: https://osv.dev/vulnerability/CVE-2026-6621

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6621/
Summaries are generated and may contain mistakes; the official description above is the record.