CVE-2021-47735: CMSimple 5.4 contains an authenticated remote code execution vulnerability that allows logged-in attackers to

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HIGH 8.8DOWNGRADE

CVE-2021-47735 is a high-severity flaw (CVSS 8.8) affecting cmsimple. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

CMSimple 5.4 contains an authenticated remote code execution vulnerability that allows logged-in attackers to inject malicious PHP code into template files. Attackers can exploit the template editing functionality by crafting a reverse shell payload and saving it through the template editing endpoint with a valid CSRF token.

Why this priority

High severity
Public exploit reference

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

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.9% (top 41%)
CISA exploited list	No
Weakness	CWE-94
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-2021-47735?

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

Is CVE-2021-47735 being exploited?

CVE-2021-47735 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-2021-47735 affect?

CVE-2021-47735 affects cmsimple. Severity is high (CVSS 8.8). CMSimple 5.4 contains an authenticated remote code execution vulnerability that allows logged-in attackers to inject malicious PHP code into template files. Attackers can exploit the template editing functionality by crafting a reverse shel

How urgent is CVE-2021-47735?

Priority 51/100. High severity; Public exploit reference

Software pages

PHP vulnerabilities

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References

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