CVE-2020-21474: File Upload vulnerability in NucleusCMS v.3.71 allows a remote attacker to execute arbitrary code via the /nuc

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2020-21474 is a critical-severity flaw (CVSS 9.8) affecting nucleuscms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

File Upload vulnerability in NucleusCMS v.3.71 allows a remote attacker to execute arbitrary code via the /nucleus/plugins/skinfiles/?dir=rsd parameter.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.2% (top 33%)
CISA exploited list	No
Weakness	CWE-434
Published	2023-06-20
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: nucleuscms

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-06-20 15:15 UTCPublished CVE record published
2026-06-17 03:03 UTCUpdated Record last modified

nucleuscms nucleuscms DOWNGRADE

Affected: 3.71

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.71

1. Check installed version

apt-cache policy nucleuscms || rpm -q nucleuscms || nucleuscms --version

2. No fixed release: DOWNGRADE to a release before 3.71 (Debian / Ubuntu)

apt-cache madison nucleuscms sudo apt install nucleuscms=<VERSION_BEFORE_3.71> sudo apt-mark hold nucleuscms

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nucleuscms sudo dnf downgrade nucleuscms-<VERSION_BEFORE_3.71> sudo dnf versionlock add nucleuscms

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-2020-21474?

nucleuscms: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-21474 being exploited?

CVE-2020-21474 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-2020-21474 affect?

CVE-2020-21474 affects nucleuscms. Severity is critical (CVSS 9.8). File Upload vulnerability in NucleusCMS v.3.71 allows a remote attacker to execute arbitrary code via the /nucleus/plugins/skinfiles/?dir=rsd parameter.

How urgent is CVE-2020-21474?

Priority 61/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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