CVE-2021-3243: Wfilter ICF 5.0.117 contains a cross-site scripting (XSS) vulnerability

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MEDIUM 6.1DOWNGRADE

CVE-2021-3243 is a medium-severity flaw (CVSS 6.1) affecting wfilter internet content filter. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Wfilter ICF 5.0.117 contains a cross-site scripting (XSS) vulnerability. An attacker in the same LAN can craft a packet with a malicious User-Agent header to inject a payload in its logs, where an attacker can take over the system by through its plugin-running function.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-04-15
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: wfiltericf

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

Am I affected?

Timeline

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

wfiltericf wfilter internet content filter DOWNGRADE

Affected: 5.0.117

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.0.117

1. Check installed version

apt-cache policy wfilter-internet-content-filter || rpm -q wfilter-internet-content-filter || wfilter-internet-content-filter --version

2. No fixed release: DOWNGRADE to a release before 5.0.117 (Debian / Ubuntu)

apt-cache madison wfilter-internet-content-filter sudo apt install wfilter-internet-content-filter=<VERSION_BEFORE_5.0.117> sudo apt-mark hold wfilter-internet-content-filter

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

dnf --showduplicates list wfilter-internet-content-filter sudo dnf downgrade wfilter-internet-content-filter-<VERSION_BEFORE_5.0.117> sudo dnf versionlock add wfilter-internet-content-filter

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-2021-3243?

wfilter internet content filter: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-3243 being exploited?

CVE-2021-3243 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-2021-3243 affect?

CVE-2021-3243 affects wfilter internet content filter. Severity is medium (CVSS 6.1). Wfilter ICF 5.0.117 contains a cross-site scripting (XSS) vulnerability. An attacker in the same LAN can craft a packet with a malicious User-Agent header to inject a payload in its logs, where an attacker can take over the system by throug

How urgent is CVE-2021-3243?

Priority 40/100. Public exploit reference

References

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