PatchTheCVECVE-2021-36763: In CODESYS V3 web server before 3.5.17.10, files or directories are accessible to External Parties.
48
This month
HIGH 7.5REMOTEUPGRADEUPGRADEUPGRADE
CVE-2021-36763 is a high-severity flaw (CVSS 7.5) affecting control, control, control. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
In CODESYS V3 web server before 3.5.17.10, files or directories are accessible to External Parties.
Why this priority
- High severity
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.5 (High) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 1.2% (top 33%) |
| CISA exploited list | No |
| Weakness | CWE-552 |
| Published | 2021-08-03 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
codesys control UPGRADE
Affected: < 4.2.0.0
Fixed in: 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
codesys control UPGRADE
Affected: < 4.2.0.0
Fixed in: 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
codesys control UPGRADE
Affected: < 4.2.0.0
Fixed in: 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
codesys control UPGRADE
Affected: <= 4.2.0.0
Fixed in: newer than 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to newer than 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
codesys control UPGRADE
Affected: < 4.2.0.0
Fixed in: 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
codesys control UPGRADE
Affected: < 4.2.0.0
Fixed in: 4.2.0.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy control || rpm -q control || control --version
2. UPGRADE to 4.2.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade control
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade control
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
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.
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-2021-36763?
control: upgrade to 4.2.0.0; control: upgrade to 4.2.0.0; control: upgrade to 4.2.0.0. Exact commands for each OS are on this page.
Is CVE-2021-36763 being exploited?
CVE-2021-36763 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-2021-36763 affect?
CVE-2021-36763 affects control, control, control. Severity is high (CVSS 7.5). In CODESYS V3 web server before 3.5.17.10, files or directories are accessible to External Parties.
How urgent is CVE-2021-36763?
Priority 48/100. High severity; Remotely exploitable, no login, no user action
Related CVEs
- CVE-2023-25719 HIGH 8.8 UPGRADE ConnectWise Control before 22.9.10032 (formerly known as ScreenConnect) fails to validate user-supplied parame
- CVE-2023-25718 CRITICAL 9.8 UPGRADE In ConnectWise Control through 22.9.10032 (formerly known as ScreenConnect), after an executable file is signe
- CVE-2021-33485 CRITICAL 9.8 UPGRADE UPGRADE CODESYS Control Runtime system before 3.5.17.10 has a Heap-based Buffer Overflow.
- CVE-2019-16517 CRITICAL 9.8 DOWNGRADE An issue was discovered in ConnectWise Control (formerly known as ScreenConnect) 19.3.25270.7185
- CVE-2019-16516 MEDIUM 5.3 UPGRADE An issue was discovered in ConnectWise Control (formerly known as ScreenConnect) 19.3.25270.7185