CVE-2021-47733: CMSimple 5.4 contains a cross-site scripting vulnerability that allows attackers to bypass input filtering by

Routine

MEDIUM 6.1DOWNGRADE

CVE-2021-47733 is a medium-severity flaw (CVSS 6.1) affecting cmsimple. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

CMSimple 5.4 contains a cross-site scripting vulnerability that allows attackers to bypass input filtering by using HTML to Unicode encoding. Attackers can inject malicious scripts by encoding payloads like ')-alert(1)// and execute arbitrary JavaScript when victims interact with delete buttons.

Why this priority

Public exploit reference

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

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-79
Published	2025-12-23
Last modified	2026-06-17

Publisher (CNA): VulnCheck · Vendor: cmsimple

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

Am I affected?

Timeline

2025-12-23 20:15 UTCPublished CVE record published
2026-06-17 04:18 UTCUpdated Record last modified

cmsimple cmsimple DOWNGRADE

Affected: 5.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 5.4 (Debian / Ubuntu)

apt-cache madison cmsimple sudo apt install cmsimple=<VERSION_BEFORE_5.4> sudo apt-mark hold cmsimple

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

dnf --showduplicates list cmsimple sudo dnf downgrade cmsimple-<VERSION_BEFORE_5.4> sudo dnf versionlock add cmsimple

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-2021-47733?

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

Is CVE-2021-47733 being exploited?

CVE-2021-47733 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-2021-47733 affect?

CVE-2021-47733 affects cmsimple. Severity is medium (CVSS 6.1). CMSimple 5.4 contains a cross-site scripting vulnerability that allows attackers to bypass input filtering by using HTML to Unicode encoding. Attackers can inject malicious scripts by encoding payloads like ')-alert(1)// and execute arbitra

How urgent is CVE-2021-47733?

Priority 31/100. Public exploit reference

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References

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