CVE-2021-4451: The NinjaFirewall plugin for WordPress is vulnerable to Authenticated PHAR Deserialization in versions up to,

Q: How do I fix CVE-2021-4451?

ninjafirewall: upgrade to newer than 4.3.3. Exact commands for each OS are on this page.

Q: Is CVE-2021-4451 being exploited?

CVE-2021-4451 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-2021-4451 affect?

CVE-2021-4451 affects ninjafirewall. Severity is medium (CVSS 6.6). The NinjaFirewall plugin for WordPress is vulnerable to Authenticated PHAR Deserialization in versions up to, and including, 4.3.3. This allows authenticated attackers to perform phar deserialization on the server. This deserialization can

Q: How urgent is CVE-2021-4451?

Priority 36/100. No elevated risk signals yet.

Routine

MEDIUM 6.6UPGRADE

CVE-2021-4451 is a medium-severity flaw (CVSS 6.6) affecting ninjafirewall. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The NinjaFirewall plugin for WordPress is vulnerable to Authenticated PHAR Deserialization in versions up to, and including, 4.3.3. This allows authenticated attackers to perform phar deserialization on the server. This deserialization can allow other plugin or theme exploits if vulnerable software is present (WordPress, and NinjaFirewall).

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	High
User interaction	None
EPSS exploit chance	0.6% (top 50%)
CISA exploited list	No
Weakness	CWE-502
Published	2024-10-16
Last modified	2026-06-17

Publisher (CNA): Wordfence · Vendor: nintechnet

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

Am I affected?

Timeline

2024-10-16 07:15 UTCPublished CVE record published
2026-06-17 04:19 UTCUpdated Record last modified

nintechnet ninjafirewall UPGRADE

Affected: <= 4.3.3

Fixed in: newer than 4.3.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ninjafirewall || rpm -q ninjafirewall || ninjafirewall --version

2. UPGRADE to newer than 4.3.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ninjafirewall

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ninjafirewall

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.

Quick answers

How do I fix CVE-2021-4451?

ninjafirewall: upgrade to newer than 4.3.3. Exact commands for each OS are on this page.

Is CVE-2021-4451 being exploited?

CVE-2021-4451 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-2021-4451 affect?

CVE-2021-4451 affects ninjafirewall. Severity is medium (CVSS 6.6). The NinjaFirewall plugin for WordPress is vulnerable to Authenticated PHAR Deserialization in versions up to, and including, 4.3.3. This allows authenticated attackers to perform phar deserialization on the server. This deserialization can

How urgent is CVE-2021-4451?

Priority 36/100. No elevated risk signals yet.

Software pages

WordPress vulnerabilities

References

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