CVE-2021-26740: Arbitrary file upload vulnerability sysupload.php in millken doyocms 2.3 allows attackers to execute arbitrary

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-26740 is a critical-severity flaw (CVSS 9.8) affecting doyocms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Arbitrary file upload vulnerability sysupload.php in millken doyocms 2.3 allows attackers to execute arbitrary code.

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	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-434
Published	2021-11-01
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: doyocms project

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

Am I affected?

Timeline

2021-11-01 16:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

doyocms project doyocms DOWNGRADE

Affected: 2.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.3

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.3 (Debian / Ubuntu)

apt-cache madison doyocms sudo apt install doyocms=<VERSION_BEFORE_2.3> sudo apt-mark hold doyocms

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

dnf --showduplicates list doyocms sudo dnf downgrade doyocms-<VERSION_BEFORE_2.3> sudo dnf versionlock add doyocms

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-2021-26740?

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

Is CVE-2021-26740 being exploited?

CVE-2021-26740 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-2021-26740 affect?

CVE-2021-26740 affects doyocms. Severity is critical (CVSS 9.8). Arbitrary file upload vulnerability sysupload.php in millken doyocms 2.3 allows attackers to execute arbitrary code.

How urgent is CVE-2021-26740?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

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References

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