# CVE-2026-42171: Privilege escalation in Nullsoft Scriptable Install System

> Local attackers can escalate privileges by exploiting insecure temp directory usage in NSIS when running as SYSTEM.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 25 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-42171, GHSA-594m-24qw-wfmp, UBUNTU-CVE-2026-42171

## What is CVE-2026-42171?

CVE-2026-42171 is a high-severity vulnerability in Nullsoft Scriptable Install System, published on 24 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

NSIS (Nullsoft Scriptable Install System) 3.06.1 before 3.12 sometimes uses the Low IL temp directory when executing as SYSTEM, allowing local attackers to gain privileges (if they can cause my_GetTempFileName to return 0, as shown in the references).

Weakness: CWE-427 (Uncontrolled Search Path Element)

## Which versions are affected by CVE-2026-42171?

It affects 1 product.


Products: Nullsoft Nullsoft Scriptable Install System.

## How do I fix CVE-2026-42171?

Upgrade to a fixed version.

## Is CVE-2026-42171 being exploited?

There is no known exploitation of CVE-2026-42171 in the wild and no public exploit code.

## Other vulnerabilities in Nullsoft Scriptable Install System

- [CVE-2023-37378](https://insights.sbomify.com/CVE-2023-37378/): Missing authorization in n/a (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42171 and fix it if it is affected.

What it is: CVE-2026-42171 is a high-severity vulnerability in Nullsoft Scriptable Install System, published on 24 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-42171 in the wild and no public exploit code.

Affected product: Nullsoft Scriptable Install System. 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-2026-42171/ (Markdown: https://insights.sbomify.com/CVE-2026-42171/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42171
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42171
- OSV: https://osv.dev/vulnerability/CVE-2026-42171

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42171/
Summaries are generated and may contain mistakes; the official description above is the record.