CVE-2020-21865: ThinkPHP50-CMS v1.0 contains a remote code execution (RCE) vulnerability in the component /public/?s=captcha.

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2020-21865 is a critical-severity flaw (CVSS 9.8) affecting thinkphp50-cms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

ThinkPHP50-CMS v1.0 contains a remote code execution (RCE) vulnerability in the component /public/?s=captcha.

Why this priority

Critical severity
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	2.0% (top 19%)
CISA exploited list	No
Published	2021-10-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: thinkphp50-cms project

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

Am I affected?

Timeline

2021-10-07 21:15 UTCPublished CVE record published
2026-06-17 03:03 UTCUpdated Record last modified

thinkphp50-cms project thinkphp50-cms DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

apt-cache policy thinkphp50-cms || rpm -q thinkphp50-cms || thinkphp50-cms --version

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison thinkphp50-cms sudo apt install thinkphp50-cms=<VERSION_BEFORE_1.0> sudo apt-mark hold thinkphp50-cms

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

dnf --showduplicates list thinkphp50-cms sudo dnf downgrade thinkphp50-cms-<VERSION_BEFORE_1.0> sudo dnf versionlock add thinkphp50-cms

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-2020-21865?

thinkphp50-cms: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-21865 being exploited?

CVE-2020-21865 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-2020-21865 affect?

CVE-2020-21865 affects thinkphp50-cms. Severity is critical (CVSS 9.8). ThinkPHP50-CMS v1.0 contains a remote code execution (RCE) vulnerability in the component /public/?s=captcha.

How urgent is CVE-2020-21865?

Priority 60/100. Critical severity; Remotely exploitable, no login, no user action

References

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