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

Q: How do I fix CVE-2020-35729?

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

Q: Is CVE-2020-35729 being exploited?

CVE-2020-35729 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-2020-35729 affect?

CVE-2020-35729 affects klog server. Severity is critical (CVSS 9.8). KLog Server 2.4.1 allows OS command injection via shell metacharacters in the actions/authenticate.php user parameter.

Q: How urgent is CVE-2020-35729?

Priority 69/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2020-35729 is a critical-severity flaw (CVSS 9.8) affecting klog server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

KLog Server 2.4.1 allows OS command injection via shell metacharacters in the actions/authenticate.php user parameter.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	88.1% (top 1%)
CISA exploited list	No
Weakness	CWE-78
Published	2020-12-27
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

2020-12-27 05:15 UTCPublished CVE record published
2026-06-17 03:14 UTCUpdated Record last modified

klogserver klog server DOWNGRADE

Affected: 2.4.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.4.1

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.4.1 (Debian / Ubuntu)

apt-cache madison klog-server sudo apt install klog-server=<VERSION_BEFORE_2.4.1> sudo apt-mark hold klog-server

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

dnf --showduplicates list klog-server sudo dnf downgrade klog-server-<VERSION_BEFORE_2.4.1> sudo dnf versionlock add klog-server

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · root · FIXED · 6.40.04-7.fc46 · FEDORA-2026-7329868400 · source

sudo dnf upgrade --advisory=FEDORA-2026-7329868400

Public exploits and detection

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

GitHub PoC: Al1ex/CVE-2020-35729 (5 stars)
Exploit-DB: Klog Server 2.4.1 - Command Injection (Unauthenticated)
Exploit-DB: Klog Server 2.4.1 - Unauthenticated Command Injection (Metasploit)
Metasploit: Klog Server authenticate.php user Unauthenticated Command Injection
Nuclei scan template: Klog Server <=2.41 - Unauthenticated Command Injection

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-2020-35729?

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

Is CVE-2020-35729 being exploited?

CVE-2020-35729 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-2020-35729 affect?

CVE-2020-35729 affects klog server. Severity is critical (CVSS 9.8). KLog Server 2.4.1 allows OS command injection via shell metacharacters in the actions/authenticate.php user parameter.

How urgent is CVE-2020-35729?

Priority 69/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

Related CVEs

CVE-2021-3317 HIGH 8.8 UPGRADE KLog Server through 2.4.1 allows authenticated command injection

References

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