# CVE-2026-26021: Prototype pollution in set-in

> Prototype pollution in set-in allows attackers to modify Object.prototype via crafted input, potentially leading to code execution or privilege escalation.

- **Severity:** Critical 9.4 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Feb 2026
- **Updated:** 12 Feb 2026
- **Also known as:** GHSA-2c4m-g7rx-63q7

## What is CVE-2026-26021?

CVE-2026-26021 is a critical code injection vulnerability in ahdinosaur set-in, published on 11 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

set-in provides the set value of nested associative structure given array of keys. A prototype pollution vulnerability exists in the the npm package set-in (>=2.0.1, < 2.0.5). Despite a previous fix that attempted to mitigate prototype pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using Array.prototype. This has been fixed in version 2.0.5.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-26021?

2 open source packages ship an affected version, including set-in. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `set-in` | npm | From 2.0.1 | 2.0.5 |
| `set-in` | npm | From 2.0.1 | 2.0.5 |

Products: Set-in Project Set-In.

## How do I fix CVE-2026-26021?

Upgrade set-in to 2.0.5 or later.

## Is CVE-2026-26021 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-26021 exists.

## Other vulnerabilities in ahdinosaur set-in

- [CVE-2020-28273](https://insights.sbomify.com/CVE-2020-28273/): Prototype pollution in set-in (critical 9.8)
- [CVE-2022-25354](https://insights.sbomify.com/CVE-2022-25354/): Prototype Pollution (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-26021 and fix it if it is affected.

What it is: CVE-2026-26021 is a critical code injection vulnerability in ahdinosaur set-in, published on 11 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-26021 exists.

Affected packages and fixed versions:
- set-in (npm): affected from 2.0.1; fixed in 2.0.5
- set-in (npm): affected from 2.0.1; fixed in 2.0.5

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-2026-26021/ (Markdown: https://insights.sbomify.com/CVE-2026-26021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-26021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-26021
- OSV: https://osv.dev/vulnerability/CVE-2026-26021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-26021/
Summaries are generated and may contain mistakes; the official description above is the record.