CVE-2026-42171: NSIS (Nullsoft Scriptable Install System) 3.06.1 before 3.12 sometimes uses the Low IL temp directory when exe

Routine

HIGH 7.8UPGRADE

CVE-2026-42171 is a high-severity flaw (CVSS 7.8) affecting nullsoft scriptable install system. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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).

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 89%)
CISA exploited list	No
Weakness	CWE-427
Published	2026-04-24
Last modified	2026-10-26

Publisher (CNA): MITRE · Vendor: nullsoft

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-24 22:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

nullsoft nullsoft scriptable install system UPGRADE

Affected: >= 3.06.1 and < 3.12

Fixed in: 3.12

Safe to downgrade to: a release before 3.06.1

1. Check installed version

apt-cache policy nullsoft-scriptable-install-system || rpm -q nullsoft-scriptable-install-system || nullsoft-scriptable-install-system --version

2. UPGRADE to 3.12 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nullsoft-scriptable-install-system

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nullsoft-scriptable-install-system

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.06.1 (Debian / Ubuntu)

apt-cache madison nullsoft-scriptable-install-system sudo apt install nullsoft-scriptable-install-system=<VERSION_BEFORE_3.06.1> sudo apt-mark hold nullsoft-scriptable-install-system

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nullsoft-scriptable-install-system sudo dnf downgrade nullsoft-scriptable-install-system-<VERSION_BEFORE_3.06.1> sudo dnf versionlock add nullsoft-scriptable-install-system

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42171?

nullsoft scriptable install system: upgrade to 3.12. Exact commands for each OS are on this page.

Is CVE-2026-42171 being exploited?

CVE-2026-42171 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42171 affect?

CVE-2026-42171 affects nullsoft scriptable install system. Severity is high (CVSS 7.8). 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 r

How urgent is CVE-2026-42171?

Priority 30/100. High severity

References

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