CVE-2021-3317: KLog Server through 2.4.1 allows authenticated command injection

Q: How do I fix CVE-2021-3317?

klog server: upgrade to newer than 2.4.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-3317 being exploited?

CVE-2021-3317 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-3317 affect?

CVE-2021-3317 affects klog server. Severity is high (CVSS 8.8). KLog Server through 2.4.1 allows authenticated command injection. async.php calls shell_exec() on the original value of the source parameter.

Q: How urgent is CVE-2021-3317?

Priority 60/100. High severity; EPSS top 1%: very likely to be exploited; Public exploit reference

This week

HIGH 8.8UPGRADE

CVE-2021-3317 is a high-severity flaw (CVSS 8.8) affecting klog server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

KLog Server through 2.4.1 allows authenticated command injection. async.php calls shell_exec() on the original value of the source parameter.

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	41.4% (top 1%)
CISA exploited list	No
Weakness	CWE-78
Published	2021-01-26
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: klogserver

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

Am I affected?

Timeline

2021-01-26 23:15 UTCPublished CVE record published
2026-06-17 04:04 UTCUpdated Record last modified

klogserver klog server UPGRADE

Affected: <= 2.4.1

Fixed in: newer than 2.4.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy klog-server || rpm -q klog-server || klog-server --version

2. UPGRADE to newer than 2.4.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade klog-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade klog-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Klog Server 2.4.1 - Command Injection (Authenticated)

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-2021-3317?

klog server: upgrade to newer than 2.4.1. Exact commands for each OS are on this page.

Is CVE-2021-3317 being exploited?

CVE-2021-3317 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-2021-3317 affect?

CVE-2021-3317 affects klog server. Severity is high (CVSS 8.8). KLog Server through 2.4.1 allows authenticated command injection. async.php calls shell_exec() on the original value of the source parameter.

How urgent is CVE-2021-3317?

Priority 60/100. High severity; EPSS top 1%: very likely to be exploited; Public exploit reference

Software pages

PHP vulnerabilities

Related CVEs

CVE-2020-35729 CRITICAL 9.8 DOWNGRADE KLog Server 2.4.1 allows OS command injection via shell metacharacters in the actions/authenticate.php user pa

References

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