CVE-2021-47734: CMSimple 5.4 contains an authenticated local file inclusion vulnerability that allows remote attackers to mani

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HIGH 7.8DOWNGRADE

CVE-2021-47734 is a high-severity flaw (CVSS 7.8) 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 local file inclusion vulnerability that allows remote attackers to manipulate PHP session files and execute arbitrary code. Attackers can leverage the vulnerability by changing the functions file path and uploading malicious PHP code through session file upload mechanisms.

Why this priority

High severity
Public exploit reference

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

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.8% (top 44%)
CISA exploited list	No
Weakness	CWE-98
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-2021-47734?

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

Is CVE-2021-47734 being exploited?

CVE-2021-47734 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-2021-47734 affect?

CVE-2021-47734 affects cmsimple. Severity is high (CVSS 7.8). CMSimple 5.4 contains an authenticated local file inclusion vulnerability that allows remote attackers to manipulate PHP session files and execute arbitrary code. Attackers can leverage the vulnerability by changing the functions file path

How urgent is CVE-2021-47734?

Priority 46/100. High severity; Public exploit reference

Software pages

PHP vulnerabilities

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References

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